PHILADELPHIA — A fielding blunder cost the Pittsburgh Pirates an important game in the middle of their playoff chase.

Maikel Franco hit a tiebreaking single in the seventh inning, Freddy Galvis was a triple shy of the cycle and the Phillies beat the Pirates 4-3 on Tuesday night.

The Phillies took a 1-0 lead in the first on Chase Utley’s RBI single. Franco hit a popup to shallow right that fell for a double when second baseman Neil Walker couldn’t see it in the lights.

It ended up costing the Pirates, who entered the night with a 1 1/2-game lead over Atlanta and Milwaukee for the second NL wild card.

“It was a tight, well-pitched game, but we gifted them a run,” Pirates manager Clint Hurdle said.

Pittsburgh also lost a run after a video review showed that a fan reached over the fence and touched Starling Marte’s drive to left-center in the fifth. Marte was awarded a double instead of a homer and was stranded at third.

“It went to their advantage,” Hurdle said.

Pirates starter Edinson Volquez gave up three runs and six hits in six innings. He wasn’t pleased to leave the game early.

“I threw 90 pitches. He took me out,” said a frustrated Volquez, who actually threw 92.

Galvis homered, doubled and scored the go-ahead run after an infield single and a stolen base. Justin De Fratus (3-1) pitched a scoreless inning for the win. Jonathan Papelbon finished for his 36th save in 39 chances.

Galvis led off the seventh with a grounder to deep shortstop for a single off Justin Wilson (3-4). After a pair of strikeouts, Galvis stole second. He scored on Franco’s hit to right.

“An infield single and a seeing-eye single,” Hurdle said.

Galvis hit a drive way out to right to tie it at 3 in the fifth.

“I was behind in the count and I paid for it,” Volquez said. “He wanted a fastball down the middle and he got it.”

Jordy Mercer’s RBI double in the second tied it at 1. Russell Martin hit a two-run double to right, giving the Pirates a 3-2 lead in the third.

Phillies starter David Buchanan helped himself with an RBI single after Galvis hit a double off the right-field wall in the second.

Buchanan allowed three runs — two earned — and four hits in six innings.