Real Madrid kept the gap to one point with one match left when a late flurry of goals gave them a 5-1 victory at home to Athletic Bilbao, who also had a player sent off, but Barca now only need a win at home.
Barca beat arch rivals Real in both this season's "Clasicos" and have lost only once all season, scoring 94 goals and conceding 24. They extended their record points tally to 96 from 37 matches with Real in second on 95 and Valencia trailing on 68.
La Liga top scorer Messi put them in front in the fifth minute at the Sanchez Pizjuan when he controlled Maxwell's pass on his chest and drilled a low shot past goalkeeper Andres Palop for his 32nd of the season.
A sublime first-time pass from midfielder Xavi sent teenager Bojan clear to score a second for the visitors in the 28th and Barca looked to be cruising when Pedro added a third with a snap shot from the edge of the area in the 62nd.
Two Sevilla goals inside three second-half minutes from Frederic Kanoute and Luis Fabiano set Barca's nerves jangling.
The final whistle prompted wild celebrations from the Barca players and their knot of travelling fans high in the stands.
At the Bernabeu, a Gonzalo Higuain shot struck the hand of Fernando Amorebieta in the penalty area in the 20th minute and the referee showed the Bilbao defender a straight red card.
Ronaldo sent goalkeeper Gorka Iraizoz the wrong way with the spot kick but Real were stunned four minutes before the break when midfielder Fran Yeste burst clear and finished with aplomb past Iker Casillas.
With the score at 1-1 and Barca winning in Sevilla, Real's title hopes were slipping away but Higuain, Sergio Ramos substitute Karim Benzema and Marcelo struck four goals in the last 20 minutes to keep Real hot on Barca's heels.
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