Samuel Eto'o and Thierry Henry also scored for the Spanish leaders, with all goals coming in the first half. Messi also had a penalty appeal waived away in the 19th minute, and Barcelona coach Pep Guardiola was sent off for protesting.

Barcelona's victory at the Camp Nou sets up a potential matchup with Chelsea in the semifinals, after the Blues beat Liverpool 3-1 on Wednesday.

Bayern, coming off a 5-1 league loss on Saturday, looked lost as Barcelona's high-powered offense swarmed the German area from the opening moments.

Messi opened the scoring in the ninth minute, after Samuel Eto'o drew two defenders before slipping the ball into the area for the Argentina winger, who coolly rolled it past goalkeeper Hans-Jorg Butt and inside the far post.

Messi turned provider to Eto'o in a near identical buildup in the 13th. After anticipating Eto'o's run perfectly, Messi slid a quick pass into the area for the Cameroon striker to shoot through Butt's legs.

Referee Howard Webb drew Guardiola's ire after waiving away a penalty appeal when Christian Lell barged into Messi as he moved around the Bayern defender in the area. Messi was also booked for questioning the decision.

Moments later, Henry caught Butt under the right eye with his boots after sliding into the goalkeeper, and the break for medical treatment offered Bayern a breather from the Barcelona onslaught.

But two more goals shortly followed.

Lell was filling in for injured left back Phillip Lahm and had the task of marking Messi, but couldn't prevent him from sliding in to redirect Henry's pass into the net from close range in the 38th for his eighth goal in the competition.

Messi then came charging across the area in the 43rd before laying the ball off to Eto'o, who was swarmed by white shirts. But the ball popped out to Henry, who rolled it past a helpless Butt for the fourth.

Messi, Eto'o and Henry have c****ined for 89 of Barcelona's 126 goals scored this season.

Bayern coach Juergen Klinsmann opted for the 34-year-old Butt over regular keeper Michael Rensing, despite having only played once all season. But the veteran could hardly be faulted as Barcelona's attack repeatedly broke down Bayern's defense, which was also without regulars Daniel van Buyten and Lucio.

Bayern striker Luca Toni was neutralized throughout, with his best touch coming in the 45th when the Italy striker played Franck Ribery clear along the left, but the France winger sliced wide.

Butt finally got a chance to show off his skill in the 59th when he dove to tip away Messi's drive from the right. Andres Iniesta nearly curled a short drive into the top of goal a bit later.

Ribery played Ze Roberto clear into Barcelona's penalty box in the 71st but Carles Puyol hustled back to deflect the Brazilian's shot as Barcelona kept a clean sheet at home for the first time this season in the competition.

The Camp Nou hasn't been kind to Bayern, with the Germans allowing two injury-time goals to lose the 1999 Champions League final to Manchester United here. Wednesday's result matched the club's third-worst away defeat in UEFA competitions.

The return leg will be played at the Allianz Arena on Tuesday.