Santiago Gentiletti scored in the 87th and Ciro Rius added another two minutes later to lead Argentinos Juniors to a 2-0 victory over Boca Juniors on Saturday.
In other results Saturday; Gimnasia defeated Quilmes 1-0, Godoy Cruz and Newell's Old Boys drew 0-0 and Racing rallied for a 2-2 draw with Arsenal.
Estudiantes are the leaders in Argentina's Apertura tournament following a 3-0 victory Friday over Lanus. Estudiantes have 30 points, six more than Velez and Arsenal.
Boca's loss is sure to be a blow to coach Claudio Borghi, who has been under pressure all season and was expecting a boost with Riquelme's return. There was no hiding Borghi's anxiety as he smoked cigarettes on the bench and winced at the two late goals. He coached Argentinos to the Clausura title six months ago, moving to Boca to join one of the country's most famous clubs.
Borghi has also been mentioned as a candidate to coach Chile's national team following the resignation a few days ago of fellow Argentine Marcelo Bielsa.
Boca has only 17 points from 13 matches - Argentinos Juniors have 16 - with both lodged down deep in the standings.
The next match is even more important, with Boca facing Buenos Aires archrival River Plate on Nov. 16 in what is always the highlight of the season.
Riquelme started slowly and showed a few flashes in open play in the first half, adding to it with several dangerous corners. He was better in the second, often finding striker Martin Palermo with deft passes and nearly scoring in the 52nd when his corner hit the post.
Ariel Aguero scored for Gimnasia in the 69th in its victory over Quilmes. Quilmes stayed in last place with only six points. Gimnasia improved to nine and is in second-last place.
Racing salvaged a point on Lucas Aveldano's equalizer in the 86th minute. Racing improved to 18 points and Arsenal improved to 24.
On Friday, league-leader Estudiantes defeated Lanus 3-0 with goals from Gaston Fernandez, Michael Hoyos and Enzo Perez. The victory improved Estudiates to 30 points from 13 matches. Also Friday, Olimpo hammered Huracan with Diego Galavan, Roberto Brum, Nestor Bareiro and David Vega scoring. Both clubs are near the bottom of the table - Huracan with 13 points and Olimpo with 12.
On Sunday it's: San Lorenzo vs. Independiente, All Boys vs. River Plate, Colon vs. Tigre, Banfield vs. Velez.