BUENOS AIRES - San Lorenzo beat Tigre 2-1 in the first game of a three-way Argentine championship playoff on Wednesday, the match ending in ugly scenes as the losers protested over a red card. Play was halted for nearly six minutes in stoppage-time after Tigre goalkeeper Daniel Islas shoved his hand in the face of San Lorenzo midfielder Pablo Barrientos. Referee Saul Laverni did not see the incident but the linesman flagged and, after several minutes of deliberating and Tigre protests, Islas was sent off. Tigre supporters behind the goal threw plastic seats on to the field, delaying the game further. When play resumed, the referee, who had originally signalled four minutes of stoppage time, played one more minute and ended the match. Laverni was given police protection at the end and furious Tigre players were restrained by the coaching staff. Barrientos opened the scoring from close range in the 17th minute with his eighth goal of the championship after Islas failed to hold Santiago Solari's cross. Barrientes turned provider three minutes later when he burst down the right and Gonzalo Bergessio met his low cross with a first-time shot which flew past the startled Islas. Rank outsiders Tigre were lucky not to fall further behind when Nicolas Bianchi headed against the crossbar. On a hot afternoon at the neutral Velez Sarsfield stadium, San Lorenzo also had a penalty appeal turned down when Islas upended Bergessio in the area. But Tigre came into the game after halftime and Leandro Lazzaro pulled one back in the 76th minute, heading in a high cross from Sebastian Rusculleda. The playoff is being held after Boca Juniors, San Lorenzo and Tigre finished level on 39 points from 19 games. Goal difference is not used to settle the title in the regular tournament although it will be used in the playoff if teams finish level on points. San Lorenzo face Boca Juniors on Saturday when another win would clinch the title, and Boca meet Tigre next Tuesday. The format has been widely criticised as it could lead to a final match in which one of the two teams has nothing to play for. If San Lorenzo and Boca draw on Saturday then Tigre will be out of contention when they face Boca on Tuesday. Critics say the losers of Wednesday's game should have played Boca on Saturday to keep interest alive until the final match.