Argentina, who lead the South American group, have a bye on Friday but could secure their berth at the 2014 finals in Brazil with a victory in Asuncion on September 10.
Gago, making his first appearance of the season after recovering from injury, made a fine homecoming at La Bombonera on Sunday and laid on the opening goal for Uruguayan defender Ribair Rodriguez in the opening minute of a 2-1 victory over Velez.
Striker Ezequiel Rescaldani equalised for Velez after nine minutes and Nicolas Blandi scored the winner in the 37th. Velez had midfielder Francisco Cerro sent off in the 64th.
“I think we were more explosive in midfield because we had more ball holders, with Fernando (Gago) we owned the ball more,” Boca coach Carlos Bianchi told reporters.
“It was special because I returned to Boca’s ground after so many years,” said Gago, who left for Real Madrid in 2007.
Boca have taken nine points from five matches in the Inicial championship, first of two in the season, and are two points behind leaders Newell´s Old Boys.
The downside for Boca is that they will be without Gago and goalkeeper Agustin Orion at Olimpo next weekend when both are with Argentina, but they hope Juan Roman Riquelme can return from an injury that kept him out of Sunday’s match.
Boca’s arch-rivals River Plate had an unhappy night at San Lorenzo, going down 1-0 to a twice-taken, 62nd-minute Julio Buffarini penalty after goalkeeper Marcelo Barovero had saved the first effort but was judged to have moved early.
River have only four points after three defeats in five matches having started out as title favourites.
Racing Club, another of Argentina’s so-called Big Five clubs with Boca, River, San Lorenzo and relegated Independiente, lost 1-0 at modest All Boys and remain bottom with one point.
Former Velez and Boca coach Carlos Ischia was set to take charge at Racing on Monday after Luis Zubeldia was sacked a week ago.
As well as Gago and Orion, Sabella added three other players from the local first division after Sunday’s matches including Maxi Rodriguez of champions Newell’s to the squad he named 11 days ago.
(Reporting by Rex Gowar; editing by Justin Palmer)