Sullivan's impressive performance saw him open the scoring in first-half stoppage time with a creative back-heel flick that deflected in off the post. He then powered a shot through the legs of goalkeeper Duran Ferree from a difficult angle in the 62nd minute for a 2-0 lead. The midfielder also set up the third goal, chipping it over the defense for Frankie Westfield to run down and pass back to the penalty spot for a wide-open Bruno Damiani to score his fourth goal in two games.
Sullivan's five goals and six assists in his last seven MLS games have put him in contention for a spot in Mauricio Pochettino's squad ahead of four friendlies in the upcoming international window. Philadelphia Union (9-10-6) is unbeaten in its last 10 matches, with eight victories, since the World Cup break. San Diego (8-11-6) had a four-game home winning streak snapped.
The Union look to keep their streak going on the road against Sporting Kansas City, while San Diego travels to Florida to face Miami on Sunday.