Nationals 4, Giants 2: Adam LaRoche delivered a go-ahead, two-run homer in the sixth inning and host Washington won the opener of the three-game series.

Tanner Roark (2-0) yielded one unearned run over two innings following a 77-minute rain delay for the win and Rafael Soriano worked a perfect ninth inning for his 30th save. The Nationals have won four straight to pull within 8 1/2 games of Cincinnati in the race for the second National League wild card.

Washington broke a 1-1 tie in the sixth when Guillermo Moscoso (1-1) issued a leadoff walk to Ian Desmond and LaRoche followed with his 17th home run to the upper deck in left field. The Giants cut the lead to 3-2 on Hunter Pence’s RBI single in the seventh.

Giants starter Madison Bumgarner allowed one run on five hits over four innings and the Nationals’ Gio Gonzalez tossed four scoreless frames. Both starters were pulled after the lengthy rain delay.

Joaquin Arias had a career-high four hits for San Francisco (52-66), which left 12 runners on base and fell a season-high 14 games under .500. Desmond collected three hits for the Nationals, who added an insurance run on Kurt Suzuki’s sacrifice fly in the eighth.

GAME NOTEBOOK: Nationals LF Scott Hairston started in place of Bryce Harper, who was scratched due to flu-like symptoms. Harper was intentionally walked as a pinch-hitter in the eighth and remained in the game. … Giants 2B Marco Scutaro was scratched from the starting lineup with back stiffness. … Soriano reached the 30-save mark for the third time in his career.