SAN FRANCISCO: The Washington Nationals stayed alive in the Major League Baseball playoffs on Monday with a 4-1 victory over the San Francisco Giants.

Doug Fister pitched seven scoreless innings for the Nationals, who built the best record in the National League in the regular season but were on the brink of elimination after dropping the first two games of this best-of-five Divisional Series at home in Washington.

Now they’re two-games-to-one up in the series, with the winner to take on either St. Louis or the Los Angeles Dodgers for the National League title and a World Series berth.

After the Cardinals and Dodgers split their first two games in Los Angeles, St. Louis triumphed 3-1 at home on Monday to move within one win of advancing.

In San Francisco, the Nationals bounced back after blowing a lead in the ninth inning on the way to a devastating 18-inning defeat in Game 2 on Saturday.

Giants starting pitcher Madison Bumgarner gave up six hits and struck out six over seven innings — and his key defensive error helped the Nationals score the first two runs of the contest.

His errant throw to third base on Wilson Ramos’ seventh-inning sacrifice bunt enabled two runs to score.

Washington’s Asdrubal Cabrera then came to the plate, and his single scored Ramos to give the Nats a 3-0 lead.

Giants manager Bruce Bochy said Bumgarner’s decision to throw to third, rather than making the safer throw for an out at first, was regrettable — and so was the poor throw that was out of third baseman Pablo Sandoval’s reach and ended up in foul territory.

“He tried to do a little too much there on that bunt,” Bochy said. “He pitched great. That was not a good decision. I’m sure he wishes he could have it back.”

Bryce Harper added a solo home run to lead off the ninth inning to stretch the visitors’ lead.

Giants shortstop Brandon Crawford’s sacrifice fly to score Pablo Sandoval in the bottom of the ninth was too little for San Francisco.

San Francisco saw their post-season winning streak end at 10 games — a run dating back to the 2012 National League Championship Series.

But they’ll get another chance to wrap up the series at home on Tuesday.

In St. Louis, second baseman Kolten Wong belted a two-run home run in the seventh inning to lift the Cardinals.

catcher Yadier Molina had greeted Dodgers relief pitcher Scott Elbert with a leadoff double down the left-field line and advanced to third on a sacrifice bunt.

The first pitch of the next at-bat proved to be the difference, as Wong crushed Elbert’s slider.

“I just wanted to make sure I hit something in the air,” Wong said, “something deep enough where we could score Yadi.”

The ball landed in the Cardinals bullpen, whose relievers pitched the final two innings to finish the job started by stellar starter John Lackey.

Lackey, the only starting pitcher to win two World Series clinching games with two different teams, struck out eight over seven innings and allowed just one run on five hits.

“He’s got a great mix of intensity but still being able to keep himself under control in big situations,” Cardinals manager Mike Matheny said of Lackey. “I thought his stuff looked sharp today. I thought it was one of his best outings for us.”

Matt Carpenter hit his third home run of the series for the Cardinals, who will try to wrap up the series on Tuesday.

Carpenter’s home run came off of the Dodgers’ South Korean starter Ryu Hyun-Jin, who delivered a tasty fastball that Carpenter belted into the seats in right centerfield.

The Dodgers answered in the sixth, when Yasiel Puig ended a dismal string of seven straight strikeouts with a triple, and scored two outs later on Hanley Ramirez’s line drive.

The home run by Carpenter was the only mistake made by Ryu, who allowed five hits over six innings and showed no sign of the back and shoulder injuries that hindered him late in the regular season.