San Lorenzo took a giant stride towards their first Libertadores Cup final with a thumping 5-0 home victory over Bolivar in the first leg of their semi-final at the Nuevo Gasometro.
The Argentine side's finishing was brilliant with five goals from seven shots on target as they sought a decisive win before facing the Bolivians at high altitude in next week's second leg in La Paz.
Striker Mauro Matos put the Saints in front after six minutes when he rose unchallenged to head playmaker Leandro Romagnoli's free kick past static goalkeeper Romel Quinonez.
Left back Emmanuel Mas increased the lead before half an hour was up, heading home another free kick from Romagnoli, who would not have been playing if his ban for a red card in the quarter-final against Cruzeiro had not been lifted after CONMEBOL ruled there had been a refereeing error.
Bolivar went close with two chances early in the second half but midfielder Juan Mercier made it 3-0 on 70 minutes after a run from inside his own half. Right back Julio Buffarini struck a brilliant fourth goal four minutes later, controlling a high clearance, advancing 10 metres and firing the ball home from outside the box.
Mas completed the rout in the 87th minute with his second goal, a header from a cross swung in by substitute midfielder Pablo Barrientos, back at the club after leaving Italy's Catania.
Nacional of Paraguay beat Uruguay's Defensor Sporting 2-0 in Tuesday's first leg of the other semi-final at the Defensores del Chaco in Asuncion.