PITTSBURGH (AP) -- San Diego's Logan Forsythe and Rene Rivera delivered consecutive RBI singles in the ninth inning off Pittsburgh closer Mark Melancon and the Padres rallied for a 3-2 victory on Wednesday night.
Forsythe's single to right scored pinch-runner Andrew Cashner to tie the game and Rivera's blooper brought home Chris Denorfia as the Padres sent the Pirates to their third straight defeat. Dale Thayer (3-5) picked up the win in relief. Huston Street pitched a perfect ninth for his 33rd save.
Melancon (2-2), who inherited the closer's role when All-Star Jason Grilli went out with a forearm injury in July, blew his third save of the season.
Andrew McCutchen hit a two-run homer in the seventh to give the Pirates the lead but Pittsburgh fell to 74-3 when leading after eight when Melancon faltered.
Melancon has been nearly automatic since taking over for Grilli. Still, Melancon quickly ran into trouble against a team that owns the Pirates at PNC Park.
Jedd Gyorko led off with a single but Melancon settled down to retire the next two batters. Denorfia singled to put runners on the corners and Forsythe and Rivera followed with well-placed, if not exactly well-struck, singles as San Diego improved to 31-10 at PNC since it opened in 2001.
The rally spoiled McCutchen's latest heroics. Pittsburgh was handcuffed by San Diego starter Tyson Ross for 6 1-3 innings when Neil Walker reached on a wild pitch with one out in the seventh. McCutchen followed by turning on a 3-0 fastball, sending it into the seats in right-center for his 20th homer of the season.
The Pirates lit up Ross for five runs in 6 1-3 innings in San Diego a month ago but came in having scored just two runs in the first two games of the series, losses that dropped Pittsburgh behind St. Louis in the chase for the NL Central title.
Justin Morneau singled leading off the second before being erased on a double play. Ross spent the next 90 minutes toying with the Pirates. Pittsburgh only managed to get three balls to the outfield through six innings.
Ross retired Starling Marte to start the seventh and Walker swung and missed at strike three. The ball skittered away from catcher Rene Rivera and rolled to the backstop, allowing Walker to reach. Ross threw wide on three straight pitches to McCutchen, and the National League MVP candidate mashed a fastball over the heart of the plate well over the wall.
McCutchen trotted around the bases then came out for a curtain call as the suddenly energized crowd of over 27,000 roared.
Pittsburgh starter Charlie Morton rolled through eight innings. Mixing his sinker with an improved curveball in his comeback from Tommy John surgery last year, Morton tied a career-high with nine strikeouts, allowing only one run and two hits.
It wasn't quite enough as Pittsburgh's bid for its first NL Central title took another punch from the Padres.
NOTES: Pittsburgh sat C Russell Martin on Wednesday and will do so again on Thursday. Manager Clint Hurdle said he wants Martin to be well rested when the Pirates open a pivotal three-game series with Cincinnati on Friday. ... The series wraps up Thursday. Gerrit Cole (8-7, 3.33 ERA) starts for the Pirates against Ian Kennedy (6-9, 4.85).
Follow Will Graves at www.twitter.com/WillGravesAP