Bryce Eldridge launched a walk-off grand slam with no outs in the bottom of the ninth inning Wednesday afternoon as the San Francisco Giants rallied from a 9-1 deficit with 10 runs over the final two innings to shock the visiting Washington Nationals 11-10.

After Matt Chapman and Rafael Devers homered as part of a five-run eighth that got the Giants back in the game at 9-6, the Nationals added an insurance run in the top of the ninth when Curtis Mead homered off left-hander Reiver Sanmartin, who was making his San Francisco debut.

Down four, Luis Arraez and Chapman led off the last of the ninth with back-to-back doubles, closing the gap to 10-7, before Gus Varland walked Devers to bring the potential tying run to the plate.

Jung Hoo Lee then greeted left-hander Mitchell Parker (2-3) with a single, loading the bases for Eldridge, who took two balls before lofting a towering drive to right that barely cleared the brick wall at Oracle Park for the game-winner.

The homer was Eldridge's fourth of the season, making him the youngest player in major league history to hit a walk-off grand slam, 109 days younger than Roberto Clemente when he did it on July 25, 1956.

Sanmartin (1-0) struck out two and allowed one run over the final two innings on the mound.

Earlier, James Wood belted his 18th home run and Foster Griffin coasted through six innings of one-run ball as the Nationals appeared headed for a three-game series sweep.

Wood's homer, a two-run shot off Giants starter Robbie Ray in the third inning, produced the only scoring until the Nationals appeared to pull away in a four-run sixth.

After retiring the first two batters he faced in the sixth, Ray was pulled following the third of five consecutive hits. The left-hander eventually was charged with five runs on seven hits in 5 2/3 innings. He struck out three without issuing a walk.

Griffin, meanwhile, took a four-hit shutout into the last of the sixth before Chapman homered with one out. The left-hander called it a day at inning's end, having allowed one run and six hits. He struck out five with no walks.

Chapman finished 4-for-5 with two homers, a double, a single, three runs and three RBIs. His homers were Nos. 5 and 6 this season.

Devers, Lee and Eldridge all scored twice, while Arraez chipped in with a pair of hits for the Giants, who had lost five straight at home.

Daylen Lile had four hits to give him a 6-for-11 series for the Nationals, who went 4-2 on a trip to Arizona and San Francisco.