Guido Pizarro scored less than 30 seconds into the match and Diego Gonzalez scored in stoppage time as Lanus won its seventh straight, 2-0 over Belgrano on Monday in Argentina's Apertura.
Lanus had just three wins through its first nine matches this season, but with maximum points from its last seven has moved into first place in the standings on a tiebreaker over Velez Sarsfield.
Belgrano had a three-game unbeaten streak snapped, as it slipped to sixth.
Also Monday, Luis Farina scored twice as Racing downed Quilmes, 4-0, to climb into third place, and River Plate tied for the fourth time during a five-match unbeaten streak, 0-0, against Argentinos Juniors.
On Sunday, Velez had a five-game winning streak ended with a 1-0 loss against Boca Juniors, as Santiago Silva scored on the half-hour mark. While Velez lost the top spot, Boca moved to fifth on the strength of a six-game unbeaten run.
Fourth-place Newell's lost its first match of the season, 2-1 at home against All Boys, which got goals from Jonathan Ferrari and Mauro Matos on Sunday.
Also Sunday, Emilio Zelaya scored twice as Arsenal downed nine-man Godoy Cruz, 3-0, Lucas Mugni and Emmanuel Gigliotti scored as Colon beat Union, 2-0, in a match featuring three red cards, and Mariano Echeverria scored the tying goal as Tigre and San Martin finished, 2-2.
On Saturday, Denis Stracqualursi scored as San Lorenzo edged Atletico Rafaela, 1-0, and Duvan Zapata and Guido Carrillo scored to lift Estudiantes to a 2-0 win over Independiente.