The captain admitted that the Ligue 1 champions had dominated every area of the game and that the Blaugrana were duly condemned.
"We had a terrible day in a competition which doesn't let you off the hook," the 32-year-old said after the match.
"There was nothing positive about it, as it was all negative, especially the result.
"They were better than us at everything, in their play and in their effectiveness.
"There is no explanation for that.
"Now we have to think about the return leg and try to get closer on the scoreboard."
Pointing out that this was part of football, the midfielder also sent out a positive message of fighting to get back to winning ways, acknowledging that the fanbase was hurting too.
"Sometimes these things happen and you need to overcome them and pick yourself up again," he explained.
"We're all very frustrated right now, from the players to every last fan."
When it was put to Iniesta that the loss might have been the result of a poor attitude, he strongly disagreed with that notion.
"I have never liked discussing the word 'attitude'," he replied.
"There is no [bad attitude] linked to this team.
"This was a footballing matter.
"[Paris Saint-Germain] were better than us at playing football and at exploiting their strengths."
A home match against Leganes is next on the Catalan side's schedule as they look to bounce back in domestic competition, while the return leg of this European tie will take place on March 8.
Luis Enrique: It was a disastrous night
After a 4-0 drubbing, Barcelona coach Luis Enrique was in no mood to discuss what had happened on the pitch, his team ouplayed and his ability as coach severely questioned.
Nonetheless, despite the frustration, the Asturian boss granted opponents Paris Saint-Germain on a job well done and took responsibility for what had happened.
"It was a disasterous night," he said. "PSG was better than us with and without the ball.
"The result clearly reflects what happened and I don't need to be the one to tell cules that."
The defeat brought about a lot of criticism towards the coach, which he met with defiantly.
"Let's not waste time with easy topics," he hit out. "This is a passionate sport and there are always complications.
"The match was my responsibility.
"If you have to point fingers and single someone out, that is me as coach, since these are the same players that win on other days."
A change in system from the Blaugrana tactician didn't have its desired effect, changing a little as the Parisians continued their dominance.
"The press doesn't watch matches very closely," said a critical Luis Enrique. "We switched from a 4-3-3 to a 4-2-3-1 so Messi could get on the ball more, but it ended up like this all the same.
"I ask you [press] that your tone be the same when we lose as when we win."
The sins which condemn Luis Enrique
Barcelona have thrown away half of their season as early as February and there are several reasons for this fiasco.
To be on the brink of crashing out the Champions League in the last 16 stages when you have the likes of Lionel Messi, Luis Suarez, Neymar, Andres Iniesta and Gerard Pique in your team is the kind of thing for which heads must roll.
That starts with the coach, with Luis Enrique having been unable to solve the following problems of his team.
1. This Barcelona doesn't play at all and the tactics Unai Emery hit them with were unmatched.
Luis Enrique didn't prepare well for the match and didn't find solutions from the bench.
As he himself admitted, he is the main person responsible.
2. They don’t control matches.
It has been a long time since Barcelona failed to control matches and a long time since their midfield was repeatedly overwhelmed.
Sergio Busquets is not playing well, Iniesta has spent more time injured than he has on the pitch and nobody even understands who is the third midfielder, with Andre Gomes a disaster when he started ahead of Ivan Rakitic.
The Croatian must have done something to upset the Asturian.
3. The right-back position.
The plan for replacing Dani Alves saw Barcelona end up with Sergi Roberto, who is not a natural No.2.
Opponents know this and Luis Enrique has been unable to halt that leak on the right flank.
That lack of planning has been costly.
4. No bench.
At the start of the season there was a lot of talk about the value of Barcelona's building of a second unit, but time has put a lot of players in their place.
Players like Gomes, Lucas Digne, Samuel Umtiti, Rafinha, Denis Suarez, Arda Turan and Paco Alcacer are not the kind of players who can make a great Barcelona.
It says it all that in the middle of the Parisian debacle Luis Enrique didn't want to make his third substitution.
5. The attitude.
Sometimes a team can become cavalier when it has Messi in the lineup.
Looking at the martyrs stars, at the MSN, only Neymar comes out with some credit from a night in which Messi disappeared and Suarez was outshined by Edinson Cavani.
Zidane: Real Madrid will always be favorites in the Champions League
Napoli represents a major obstacle to Real Madrid in the Champions League last-16 although Zinedine Zidane believes his side will always be favored in the competition.
Wednesday's first leg sees Los Blancos host Maurizio Sarri's team before a trip to the Stadio San Paolo in a fortnight to decide who will pass to the quarter-finals.
"In a double-header, you know that there is a return game and at home the important thing is to stop them scoring an away goal, but I want us to be focused on what we are going to do," Zidane told reporters. "We can do damage to our opponents but they can hurt us too.
"You can win an eliminator but that doesn't mean you're going to win the Champions League, even though we are always favorites.
"It's a long hard road to victory and we are currently on it."
Despite Real's injury crisis clearing up with impeccable timing, their French coach isn't expecting Gareth Bale to make the first leg.
"It's only the first week he's been training with us and he doesn't have any ankle pain, that's the most important thing," Zidane added.
"We'll see when we finalize the squad list but we know that he's been out for three months and we have to take it slowly."
Facing off with Italian opposition, the Real boss then considered his own time in Serie A and how he grew up in the environment that Napoli have excelled this season.
"When I went to Italy, I was young but they helped me develop as a footballer," said the 44-year-old. "Because Juventus are like Real Madrid, the most important thing was to play until the last minute.
"I learned a lot there and I'm now at the biggest club in the world and I'm growing as a coach."
Modric: Thankfully Maradona isn't playing
Napoli visit the Spanish capital this midweek to take on Real Madrid in the Champions League and Luka Modric is relieved that high-profile Partenopei fan and ex-player Diego Maradona won't be on the pitch.
The Argentine has traveled to Madrid to watch the team played between 1984 and 1991 on the current holders, but the Croatian player doesn't mind the Argentine taking a seat.
"We're happy that he'll be at the [Estadio Santiago] Bernabeu," the midfielder said at Real Madrid's pre-match press conference. "Thank god he wasn't playing.
"That's why we're happy [that he'll be in the stands].
"He is one of the best players in the history of football."
Discussing the World Cup winner's former team, Modric was impressed with their good run of form and is looking forward to an intense battle in the center of the pitch.
"They are a great team, in the middle of the park and up front," he told the assembled media.
"The fight in midfield will obviously be difficult, but the important thing for us is to start the match strongly and to play well.
"They are on a good run and are playing very well. We want to show that we are also in good shape.
"We've won the past two matches, so we head into this match in a good state."
Asked whether or not Los Blancos' home first leg defeat against Celta Vigo in the Copa del Rey will influence their approach, the 31-year-old didn't think it would.
"This is a different competition, so we have to forget what happened against Celta Vigo," he replied. "We hope to avoid conceding tomorrow.
"It is a unique tournament for all Real Madrid fans.
"We hope for a good atmosphere and for the fans to support us from the beginning."
Another topic of discussion was Zinedine Zidane's recent experimenting with a 3-5-2 system, but the midfielder purchased his coach's tactics.
"I disagree," he said when asked if there were doubts about that formation.
"We also play well in that system, although that's what we do on the pitch which is really important, rather than the system.
"We have to give everything on the pitch and do as well as we can, but I believe we also did well with that system."
Gareth Bale's return was also analyzed by Los Blancos' other former Tottenham man and Modric admitted that he and his teammates are looking forward to the No.11's comeback.
"I think he has completed his recovery well," he said. "I can tell he's focused on returning as soon as possible.
"We miss him and hope he can return soon."
Finally, Modric was asked to comment on his achievement of reaching 200 Real Madrid appearances, but the Croat explained that he wants to rack up many more appearances in the club's white shirt before he leaves the Spanish capital.
Pellegrini: It looked like Guardiola was going to win the Premier League by 15 points
Former Real Madrid coach Manuel Pellegrini has insisted that there is no hard feelings from him towards his old club.
During his time in charge during the 2009/10 season, Pellegrini's side achieved a (at that time) record points tally without winning the title, with 96 not enough to overcome Barcelona.
Despite that impressive campaign, the club dispensed with its services at the end of the season, replacing the current Hebei China Fortune tactician with Jose Mourinho, with disappointing cup exits to Alcorcon and Lyon not being viewed favorably.
"Even if I had won LaLiga, my fate was the same," he told MARCA. "There is no grudge now but looking back, I would have handled things differently.
"I would have tried to have a closer relationship with the president and board after it broke down at the beginning of the year. After that, it was all very difficult.
"I do want to make clear that I have no ill will or bad feelings towards the club. It is one of my biggest sources of pride as a coach that I was in charge there and that 75 percent of people in Madrid wanted me to stay .
"On the face of it, the cup defeats are bad because it's not good for this club's image to lose but I disagree that the Alcorcon or Lyon games ultimately led to my exit."
However, in a spite of the 63-year-old's Los Blancos past, he confessed that he would have relished the opportunity to work with some of Barcelona's biggest stars of the past decade.
"I would have loved to work with Xavi Hernandez and Lionel Messi in particular," he admitted. "I was fortunate to coach Cristiano Ronaldo, a tremendous professional to have.
"He shares the same extraordinary ambition that I have but as a fan I don't like to compare them as is often the case. One is a natural talent and the other is a physical marvel."
Pellegrini is now coaching in China after his tenure at Manchester City came to an end when he announced before the end of last season that he would be replaced by Pep Guardiola.
Reflecting on the situation now, Chilean revealed that he does harbour some regret over the way things ended for him at the Etihad Stadium.
"If you ask me now if it bothered me the way things went and if I would have done something differently then I'd have to say yes," he added.
"I would have waited until the end of the season before making any announcement. It was my decision but I would have done it differently but there were just so many rumours and that bothered me."
As for his successor at Manchester City, Pellegrini mentioned the Catalan coach's fast start and subsequent troubles.
"It looked like Guardiola was going to win the Premier League by 15 points," he said. "But no, in England it doesn't work like that."