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The win saw the Catalans off to a flying start in the Champions League, avenging last season’s quarterfinal elimination by the Italian champions.
Messi broke the deadlock on the stroke of halftime by playing a slick one-two off Luis Suarez and arrowing the ball beyond Gianluigi Buffon, finally getting the better of the veteran Italian in his fourth game against him.
The Argentine was also the catalyst for the second goal,
He forced Juve to scramble the ball off the line and allowed Ivan Rakitic to shoot into an empty net in the 56th minute, adding to his strike against Juve in the 2015 Champions League final.
But Messi was far from done. For his second and Barca's third, he received a pass from Andres Iniesta and ripped more holes in a depleted Juventus defence before lashing beyond a dejected Buffon, scoring his seventh goal in three games.
Juventus, who were missing five key players including defensive warrior Giorgio Chiellini, looked a shadow of the team that beat Barca 3-0 on aggregate last season and reached the Champions League final, and have conceded seven goals in their last two games in the competition over two seasons.
Lukaku scores as United win
Romelu Lukaku opened his Champions League account as Manchester United marked their return to the competition with a 3-0 rout of Basel.
United, who missed last season's Champions League but qualified this time by winning the Europa League, dominated the first half and went ahead through Marouane Fellaini's 35th minute header.
Belgian striker Lukaku, a constant menace to the Swiss champions, scored his first Champions League goal with a textbook header soon after halftime to double United's lead.
Marcus Rashford came off the bench to score United's third goal, also his first in the competition, in the 84th minute.
Neymar leads demolition of Celtic
Paris St Germain flexed their attacking muscles with a 5-0 victory at Celtic, as the world's most expensive frontline produced a potent display of force.
Neymar, making his first European appearance for PSG after his world-record move from Barcelona, orchestrated proceedings and was joined on the scoresheet by Kylian Mbappe and Edinson Cavani, the other two members of PSG's extravagant forward trio.
The Brazilian opened the scoring in the 19th minute with an expert finish, before French striker Mbappe slammed home a second from close range and Cavani converted from the penalty spot five minutes before the break.
The visitors had to wait until the 83rd minute to add to their lead when Mikael Lustig put through his own net before Uruguayan Cavani added a fifth two minutes later with an expertly-placed header.
Chelsea crush league debutants
Chelsea enjoyed a triumphant return to the Champions League after a year out, thumping the competition's debutants Qarabag 6-0, including a stunning, if miscued, strike from new signing Davide Zappacosta.
The Azeri champions were never any match for their English counterparts and it took only five minutes for Pedro to open the scoring with a curling shot from the edge of the area.
Deadline-day signing Zappacosta, apparently looking to cross the ball, produced a swirling screamer of a goal from some 35 metres out on the half hour.
Chelsea ran riot in the second half, with goals from defender Cesar Azpilicueta, new French signing Tiemoue Bakayoko and two from Michy Batshuayi rounding off an impressive display against the Group C underdogs.
Bayern cruise to win
Bayern Munich got off to a winning start with a comfortable 3-0 victory over Anderlecht who played most of the game with 10 men at the Allianz Arena.
Striker Robert Lewandowski received a pre-match slapdown from Bayern CEO Karl-Heinz Rummenigge after criticising the club's transfer policy, but the Pole showed his value on the pitch by scoring his seventh goal in six games this season from the penalty spot after being hacked down by Sven Kums, who received a red card.
The dismissal made a daunting task become even more difficult for the visitors who went further behind on 65 minutes when Thiago Alcantara side-footed a second from a cross by Joshua Kimmich.
Niklas Suele had another effort disallowed for a foul before Kimmich rounded off the night by waltzing round the keeper to roll the ball into an empty net for Bayern's third.