Lionel Messi scored twice as Barcelona rallied from an early deficit to beat Panathinaikos 5-1 in the Champions League on Tuesday.
Three days after a surprise 2-0 Spanish league defeat to Hercules, Barcelona responded in style at the Camp Nou Stadium to start Group D play behind key playmaker Messi.
''They are unstoppable and can walk it all the way to the final,'' Panathinaikos goalkeeper Alexandros Tzorvas said. ''It's hard to compare them with anyone else.''
Sidney Govou struck for the Greek champions in the 20th minute against the run of play but Messi sprung Barcelona back two minutes later.
David Villa put the Spanish champions ahead for good in the 33rd after scoring from Sergio Busquets' flick-on. Messi notched his second in the 45th after an exquisite buildup through the middle of the field.
Tzorvas denied the Argentina forward a hat trick with a penalty-save in the 54th.
Pedro Rodriguez tapped in the fourth as the ball fell to him in the 78th after Messi's shot touched the inside of the far post.
Messi then lobbed a perfect pass to Daniel Alves as the Brazil defender strode through the area to head home the fifth on the game's last play.
''Things worked out well and it's always nice to start the Champions League with a victory,'' Pedro said. ''We knew we had to win.''
Barcelona dominated the buildup to Panathinaikos' goal but Tzorvas kept the hosts at bay by stopping Messi's third-minute header before forcing Xavi Hernandez to shoot wide from close-range three minutes later.
The Greece 'keeper then started Govou's goal. The goal kick was brilliant back-tapped on by Djibril Cisse to Govou, who swept by fellow France international Eric Abidal to go solo on Victor Valdes and beat the Barcelona goalie with a shot to the left.
''We took the lead with a beautiful goal. But they stayed calm and had essentially finished the match by the end of first half,'' Tzorvas said.
Messi quickly replied by delicately tapping Xavi's bouncing pass out of the air past Tzorvas.
Barcelona was dominating possession and applying unrelenting pressure on the Greek area with Villa well-placed to ground a shot inside the near post for his first European goal since joining the Catalan club in the summer.
Pedro headed just wide of the far post in the 35th, then Messi shot onto the underside of the crossbar two minutes later before scoring a spectacular second. Messi swapped passes with Busquets and then Pedro as he burst into the area to fire a low shot to Tzorvas' left that left him no chance.
''The third goal in the first half ended it for us,'' Tzorvas said. 'We could have pushed them higher up on the field but we defended for 75 minutes and that's what led to this.''
Messi failed to add to his tally after weakly shooting from the spot after Cedric Kante slid into him.
Pedro was well-placed to hit in the rebound from Messi's cross-goal shot that beat Tzorvas but didn't stay in.
''I just followed the play and had to push it over the goal line,'' Pedro said.
Tzorvas denied Messi in front of more than 69,000 spectators again in the 80th before Alves capped the dominant night.
FC Copenhagen beat Rubin Kazan 1-0 in the other Group D matchup.
