Peruvian Primera Division Review: Sporting Cristal beaten
Daniel Ahmed's men were beaten 3-2 at home to Union Comercio, seeing their lead at the top cut to two points.
But Alianza Lima, their nearest rivals, have played a game less and will finish top should they win their two remaining matches.
Sporting Cristal have just a game to play in the Clausura, with the top-finishing team to face Juan Aurich for the championship.
Ahmed's side went ahead in the 27th minute, capitalising on their early dominance when Irven Avila's 30-yard rocket went into the top corner.
Cristian Bogado equalised just six minutes later as his curling long-range effort looped over goalkeeper Diego Penny, who was too far off his line.
Bogado gave the visitors a shock lead with a neat finish in the 55th minute, but Cristal equalised moments later through Avila.
But with 15 minutes remaining, Juan Iglesias fired a powerful 20-yard free-kick into the roof of the net.
Alianza Lima recorded a 2-0 win at home to UTC Cajamarca.
Gabriel Costa was on hand to tap in and complete a fine team move in the 17th minute at the Estadio Alejandro Villanueva.
Mauro Guevgeozian doubled their lead just after the hour-mark with a close-range finish.
Elsewhere, Juan Aurich and Universidad San Martin drew 1-1 and Victor Pena's late brace guided Leon de Huanuco to a 2-0 win over Universitario.
Cesar Vallejo scored three times in the final quarter-hour to beat Inti Gas 3-0 and Sport Huancayo enjoyed a 3-1 win over Melgar.
Los Caimanes were 1-0 winners at Cienciano and San Simon drew 2-2 with Real Garcilaso.