© Reuters 2002

LA PAZ, Nov 6 (Reuters) - Substitute Miguel Mercado snatched an 87th minute winner to give Bolivar a 2-1 win over Argentina's San Lorenzo in the first leg of their Copa Sudamericana semi-final.

The visitors, having the usual problems in adapting to the conditions in La Paz at 3,600 metres above sea level, were agonisingly close to holding out for a draw in Tuesday night's tie before Mercado took advantage of a chance created by the tricky Luis Gatti Ribeiro.

San Lorenzo took a first-half lead when Marco Sandy, captain of the Bolivian team, put through his own goal.

Bolivar defender Oscar Sanchez equalised in the 56th minute with a 35-metre shot as San Lorenzo goalkeeper Sebastian Saja appeared to be deceived by the flight of the ball in the thin air.

The Bolivians return to Argentina - where their bus was ambushed and stoned by Gimnasia-La Plata supporters before last week's quarter-final second leg - for the away leg on November 13.

The Copa Sudamericana has replaced the Copa Mercosur and Copa Merconorte, which were both extinguished last year, but Brazilian clubs have declined to take part. Colombia's Atletico Nacional and Uruguay's Nacional meet in the other semi-final.