WASHINGTON — Bryce Harper sustained what appeared to be a serious left knee injury when he slipped on a wet first base and his left leg buckled while running out a grounder early in the Washington Nationals’ 3-1 victory against the San Francisco Giants on Saturday night.

Harper clutched at his knee while on the wet field and put no weight on his left leg as he was helped off. The 2015 NL MVP left the game immediately, and manager Dusty Baker said Harper hyperextended his knee.

“He was in obvious pain and he was praying and I was praying, too,” said manager Dusty Baker, adding that Harper would have an MRI.

“I’m asking for prayers that it’s not serious,” Baker said.

The result of the game meant little for Washington, which leads the NL East by 14½ games, or San Francisco, which is out of contention.

It didn’t begin until 7:06 p.m. after another extended weather delay, and it was raining when Harper lost his footing on a base that had water on it.

The Nationals lost catcher Wilson Ramos to a torn ACL in his right knee in late September last season, another noncontact injury that came after a rain delay in Washington.

If Harper is out, it’s a more devastating injury to the Nationals’ World Series hopes than when Ramos’ season ended prematurely a year ago.

Harper is hitting .326 with 29 home runs and 87 RBIs as the most fearsome hitter in the league.

With Harper out, the Nationals got their offense in the form of RBI doubles from Ryan Zimmerman and Adam Lind, and an RBI single from Daniel Murphy off Giants starter Jeff Samardzjia (7-12).

Right-hander Edwin Jackson (3-2) allowed one earned run on five hits and struck out five in six innings before giving way to Washington’s newfound lockdown bullpen trio of Brandon Kintzler, Ryan Madson and Sean Doolittle.

MELANCON BACK

Giants manager Bruce Bochy wanted to make sure Mark Melancon’s first appearance off the disabled list didn’t come in a high-leverage situation after the closer missed more than six weeks with a right forearm strain. He was able to do that, as Melancon allowed one hit and had one strikeout in the eighth inning, his first work since June 27.

TRAINER’S ROOM

Giants: To make room on the roster for Melancon, INF Miguel Gomez went on the 10-day DL, retroactive to Aug. 9, with right knee inflammation.