Kershaw had not allowed a run since July 5 against the New York Mets. The major league record is 59 innings, set by Orel Hershiser in 1988 with the Dodgers.
Kershaw never got comfortable after the first-inning homer, allowing four earned runs on nine hits in six innings. The Dodgers lost onPedro Alvarez's walk-off single in the 10th inning.
"It was a tough one," Kershaw said after the game. "I struggled all the way through, pretty much, and give the Pirates credit. They did a good job battling me the whole night, and I just didn't really have good stuff."
Dodgers right-hander Zack Greinke had a 43-inning scoreless streak earlier this season, which ended June 26 against the Mets.
Polanco homered to lead off the bottom of the first inning for the second straight game; he also connected off the Chicago Cubs' Dan Haren on Wednesday night. Polanco has six home runs this season.
Information from The Associated Press was used in this report.
Polanco ends Kershaw's scoreless streak
On his first pitch of the game Clayton Kershaw's scoreless innings streak ends at 37 with Gregory Polanco's home run.