PITTSBURGH — A strike away from ending his team’s longest losing streak in two years, Pittsburgh Pirates closer Tony Watson tried to get St. Louis pinch-hitter Matt Carpenter to chase a fastball up and away.

Instead, Watson’s fastball went right down the middle. Whatever chance the Pirates might have of reviving their playoff hopes may have gone along with it.

Carpenter drilled a solo shot to tie the game with two outs in the ninth and Randal Grichuk and Jhonny Peralta followed with homers of their own as the Cardinals rallied for a 9-7 win.

The Pirates have dropped eight straight and fell 5 ½ games behind St. Louis in the race for the second wild card in the National League.

“To serve up four late, it’s hard to swallow,” Watson said after blowing his third save since inheriting the closer’s role when Mark Melancon was sent to Washington at the trade deadline.

Pittsburgh had scrambled back from an early 5-0 hole to move in front with a four-run fifth inning that included Jordy Mercer’s two-run double to left. The bullpen kept the Cardinals in check and Watson quickly retired the first two hitters in the ninth and had Carpenter — who came in 2 for 17 against Watson — down 0-2 before everything changed.

“Matt Carpenter is a really good hitter, faced him a number of times,” Watson said. “Thought I could get it. Couldn’t locate the pitch ... middle up is a pretty high zone for every major league hitter.”

Things quickly unraveled from there. Yadier Molina doubled, Grichuk sent a long drive to the seats in left to put St. Louis in front and Peralta completed Watson’s implosion by depositing a 2-0 offering into the right-field seats.

“Behind in the count 2-0, you’re not getting ahead of hitters,” Watson said. “When hitters see that, balls start flying out of the park, in the gaps.”

Carpenter’s homer was the 15th by a St. Louis pinch-hitter this season, a major league record. Molina finished 4 for 5, including a first-inning grand slam. Mike Mayers (1-1) tossed a scoreless eighth for the win, and Seung-Hwan Oh worked around a solo homer to Jung Ho Kang in the ninth for his 16th save.