BARCELONA - A clearly ailing Lionel Messi came off the bench to galvanize Barcelona and help salvage a 1-1 draw with Paris St Germain on Wednesday which put the favorites through to the Champions League semifinals for a sixth straight season.

The Argentine World Player of the Year, top scorer in Europe's elite club competition the past four seasons, had only been given the all-clear shortly before kickoff after damaging a hamstring in the quarterfinal first leg 2-2 draw last week.

Coach Tito Vilanova decided to keep him in reserve but his hand was forced when Javier Pastore raced clear to give the Ligue 1 side a shock lead five minutes after halftime.

Messi replaced an ineffectual Cesc Fabregas in the 62nd minute and the buzz was palpable among almost 100,000 Barca fans packed into the giant arena on a balmy night in the Catalan capital.

Although struggling for fitness and lacking his customary zip, Messi's entrance immediately settled his teammates' nerves and restored their sense of urgency.

Barcelona's Pedro Rodriguez celebrates after scoring a goal against Paris St Germain during their Champions League quarterfinal second leg soccer match at Camp Nou stadium in Barcelona, April 10, 2013. [Photo/Agencies]

With Barca laying siege to the PSG goal and roared on by the home faithful, he fed David Villa who clipped a short pass to Pedro for his Spain teammate to lash a shot past Salvatore Sirigu from the edge of the area.

The visitors mounted several desperate attacks in a tense finale but Barca held on reasonably comfortably to advance on away goals and keep their bid for a third European crown in five years firmly on track.

"Messi made a big effort to be with us," Pedro said in an interview with Spanish television Canal Plus.

"He worked very hard this week and was able to help out the team when he came on," added the 25-year-old.

"We want to thank him, and say congratulations for everything he did to get himself ready for the game and to help the team. He's the number one.

"We felt his presence when he came on the pitch, he lifted us and we got the result."

Barca sporting Andoni Zubizarreta also paid tribute to Messi, who has been top scorer in the Champions League the past four seasons.

"We all know what Messi brings to the game, in football terms, in his ability to intimidate opponents, and for his ability to link up with others," the former Barca and Spain goalkeeper told Canal Plus.

"He wasn't at his best but he showed he could link up with others, like David (Villa), and helped get the equalizer."

Barcelona's Lionel Messi (L) and David Villa celebrate their team's goal against Paris St Germain scored by Pedro Rodriguez during their Champions League quarterfinal second leg soccer match at Camp Nou stadium in Barcelona, April 10, 2013. [Photo/Agencies]