Lionel Messi was hailed as "irreplaceable" by his Barcelona team-mates after the half-fit forward came off the substitutes' bench to inspire the team to victory over Paris St-Germain and a place in the Champions League semi-finals.

Messi did not start the match because of a hamstring injury sustained in the first leg but was summoned with Barcelona trailing 1-0 on the night, and 3-2 on aggregate, with just over an hour gone. Nine minutes later the Argentinian played a major role in constructing the equaliser, lashed in by Pedro Rodríguez, which gave the Catalan club a place in the last four on away goals.

Afterwards everyone agreed on one thing: the four-times Ballon d'Or winner had changed the game. Before he came on Barcelona had not managed a single shot on target.

The talk had been of "Messidependencia". Here it was confirmed. Messi finished the match limping slightly but Barcelona's assistant coach, Jordi Roura, said that he did not expect there to be a serious problem. If there was a risk, and the fact that he started on the bench confirmed that there was, it was one they were prepared to take. Messi will be protected between now and the semi-final; had they not gambled on his fitness here, there might be no semi-final. "If you risk, there tends to be a reward," said the sporting director, Andoni Zubizarreta.

The reward came when Messi combined with David Villa and Pedro to create the goal that put Barcelona through. "He changes the game just by his presence," said Villa. "They gained in confidence as soon as he came on," said the PSG coach, Carlo Ancelotti. "He is the best player in the world, even if he is not fully fit."

David Beckham departed satisfied at PSG's performance and admitting that he had just seen a special footballer. "Messi came on when we were 1-0 up and they scored. A player like him, 100% fit or not, will always make the difference," Beckham said. "Messi is the best player in the world, simple as that. The only player who can even get near him is Ronaldo."

Barcelona's full-back Dani Alves said: "Messi gives us a different air. We know that and so do the opposition. I prefer a crocked Messi to anyone else fully fit."

Told about Alves's remark, Roura smiled. "Well," he said, "I'd prefer him 100% fit. But it is true that tonight, despite not being fully fit, he made the difference. Obviously when a team doesn't have the best player in the world, they notice it. He is an extraordinary player and he also has that attitude and ambition which is incredible in a player of his level. You have to take your hat off to him. He is unrepeatable.

"After the goal he measured his participation, doing things in [careful] doses. His presence imposes upon the opposition. He showed his competitive spirit; he is an irreplaceable player."

No sooner had Javier Pastore's shot hit the back of the net to put PSG into the lead than Lionel Messi was pulling his socks up on the bench and heading to the touchline to warm up. "We had agreed that he would go on if we needed him," Roura said and Barcelona needed him. His presence was felt instantly.

"It is true [that he changed our mentality]," said Gerard Piqué. "We are talking about the best player in the world. It doesn't matter if he's a little bit injured: he can change everything and he did it again. Even if he's half-crippled, he's always there.

"We are really lucky and proud to have Leo in the team and we have to use him when we are struggling a little bit. For us to have Leo on the pitch is really important because he is our reference as a forward. He can score, he can pass, he can do anything. He did everything to help Pedro get the goal."

Villa admitted there was room for improvement in Barcelona's performance. "We are delighted to qualify after suffering so much," he said. "They caused us a lot of problems and they did a lot of damage with their counterattacks.

"We gave the ball away a lot, which we don't normally do; we didn't play well. We knew that they [PSG] were strong on the counterattack but they still made it difficult for us. However, we have qualified, and that's what's important."

The man Messi replaced, Cesc Fábregas, dashed away from the Camp Nou upon the final whistle. His partner gave birth to their first child, a baby girl, during the game. Her name? Lia.