Alianza Lima conceded 12 minutes from time as fourth-placed Union Comercio emerged 1-0 victors in the penultimate Peruvian Primera Division fixture at the Estadio del IPD de Moyobamba on Wednesday.
After a goalless first half, an unmarked Jesus Chavez was the hero for Union Comercio, side-footing past goalkeeper George Forsyth to seal the points 12 minutes from time.
The defeat left second-placed Alianza Lima two points adrift of leaders Sporting Cristal after 14 rounds.
Universidad San Martin - second from bottom in the table - trailed 1-0 at half-time on the back of Oscar Guerra's 31st-minute opener.
But the home side hit back, with Luis Perea equalising six minutes into the second half before Santiago Silva converted an 89th-minute penalty for Universidad San Martin's third win of the season.
Meanwhile, Leon de Huanuco extended their winning streak to four matches thanks to a 1-0 victory over Cesar Vallejo, who lost for the first time in three games.
