Kalou's future at the club is uncertain amid reports linking him with a move to Tottenham Hotspur, but he was on hand to break the deadlock by scoring his seventh goal of the season on 35 minutes.
The Ivorian international and former Chelsea striker nodded into the bottom corner from close range following a cross from Nolan Roux, but Lille's brief advantage lasted only six minutes.
Romain Alessandrini provided Doucoure with his 41st-minute equaliser, crossing low into the penalty area for his teammate to convert from eight yards and open his account for the campaign.
New Rennes signing Ola Toivenen was making his debut after signing from PSV Eindhoven, but was substituted after an hour of play, which was when the hosts began to apply pressure on the visiting goal.
Idrissa Gueye, Roux and Kalou all forced good saves from Rennes goalkeeper Benoit Costil, but it was Toivonen's replacement Nelson Oliveira who nearly snatched his side all three points when his stoppage-time shot from distance was kept out by Vincent Enyeama in the Lille net.
Lille are now nine points behind league leaders PSG, while Rennes remain 15th in the table.