Brandon Belt has belted a solo home run in the 18th inning to power San Francisco over Washington 2-1 in the longest playoff game in MLB history.

Brandon Belt smashed a solo home run in the 18th inning Saturday to power San Francisco over Washington 2-1 in the longest playoff game in Major League Baseball history.

Winning the marathon encounter, which ended just after midnight Sunday morning, gave the Giants a 2-0 lead in the best-of-five National League Division Series and San Francisco can complete a sweep with a home victory in game three on Monday.

The winner of the series will face either the Los Angeles Dodgers or St. Louis Cardinals for the National League title and a World Series berth.

The game lasted six hours and 23 minutes to shatter the previous time mark for a major league playoff game, five hours and 50 minutes, set by a 2005 Houston victory over Atlanta in 18 innings, an innings playoff record the spectacle matched.

Belt, who had been 0-for-6 at the plate, smacked a slider from Nationals relief pitcher Tanner Roark over the right-field fence to snap a deadlock that had been at 1-1 since the ninth.

"It was a hard effort by both teams," Belt said. "It was just nice to see that ball go over the fence. We're just happy to get out of it alive and go back to San Francisco."

Washington could not push across a tying run in the bottom half of the 18th and, as a result, the Nationals fell to the brink of elimination after having earlier been only one out from victory.

The Giants stretched their National League-record playoff win streak over multiple seasons to 10 games and their record road victory run to six, but only after going down to their final out in regulation play before tying the game.

"We just battled our butts off today," Belt said. "It was freaking awesome."