Lopez struck a minute before half-time to put his side within a point of leaders Lanus.
The visitors' hopes of a comeback were effectively ended when Gonzalo Contrera was sent off eight minutes from time.
Hernan Bernardello struck a last-minute equaliser as Colon Santa Fe came from two goals down to draw 3-3 with Estudiantes.
The visitors raced into a two-goal lead with goals from Maximiliano Nunez (4) and Roman Martinez (12), before Emmanuel Gigliotti pulled one back midway through the first half.
Duvan Zapata re-established the two-goal cushion from the penalty spot just after the hour mark, but Facundo Curuchet reduced the deficit in the 84th minute and Bernardello levelled in the dying moments.