Central defender Carlos Izquierdoz headed the only goal from a corner midway through the second half to secure Lanus' fifth win in six matches in which they have scored 11 goals and conceded one.
Media reports during the week said Lanus coach Guillermo Barros Schelotto and his friend and former Boca Juniors team-mate Martin Palermo, the Godoy Cruz manager, had bet a dinner on the result of the match.
"He doesn't have to pay anything," Barros Schelotto said.
Lanus, the side with a burgundy strip appropriate for a winning visit to major wine-producing province Mendoza, have 16 points to 13 for Newell's Old Boys, who knocked River Plate out of second place with a 1-0 home win.
River have 12 points and Godoy Cruz, who lost their unbeaten record, 11, level with Quilmes after their 0-0 draw with Independiente on Saturday.
River fell to a brilliant goal from Newell's Argentina striker Ignacio Scocco at the Marcelo Bielsa stadium in Rosario.
Scocco flicked the ball over Paraguayan defender Adalberto Roman on the edge of the box, headed it forward and toe-poked past advancing River goalkeeper Marcelo Barovero in the 35th minute.
Barovero was lucky to still be on the pitch having got away with what appeared to be handball outside his area when he chested the ball defending a quick Scocco break in the 12th minute.
The home side claimed Barovero had also touched the ball with his arm, which would have earned him a red card, but the referee allowed play to continue.
River had a goal disallowed in the dying minutes when striker Carlos Luna dived to head the ball into the net and the referee was about to allow it before seeing his linesman waving for handball. Luna later told reporters it had been a handball.
Former San Lorenzo coach Ricardo Caruso Lombardi was set to start his second spell in charge of struggling Argentinos Juniors away to Boca later on Sunday after being appointed in midweek to replace Gabriel Schurrer, who resigned three weeks ago.