SAN FRANCISCO (Interstat) — Matt Chapman homered twice and Bryce Eldridge hit a tying grand slam in the ninth inning as the San Francisco Giants rallied from a nine-run deficit to stun the Washington Nationals 11-10 on Wednesday afternoon at Oracle Park.

The Giants, who entered the game with a 28-41 record, scored five runs in the eighth and five more in the ninth to erase a 10-1 hole and complete the largest comeback of the season in Major League Baseball. Chapman finished 4 for 5 with two home runs and three RBIs, while Eldridge went 1 for 4 with the grand slam and four RBIs.

Washington, which dropped to 35-34, had taken command early behind starter Foster Griffin. The left-hander allowed one run on six hits over six innings, striking out five, and left with a 10-1 lead. But the Nationals’ bullpen faltered, and the Giants’ offense erupted late.

The Nationals struck first with two runs in the third inning. Keibert Ruiz singled, and James Wood followed with a two-run home run to center field, his 18th of the season. Washington extended its lead with a four-run sixth inning. Daylen Lile singled in Dylan Crews, and Nasim Nuñez drove in two more with a single. Jorbit Vivas added an RBI single, making it 6-0.

The Giants got on the board in the bottom of the sixth when Chapman hit his first home run of the game, a solo shot to left-center. But Washington answered with three runs in the seventh. James Wood walked, Curtis Mead singled, and Luis García Jr. doubled to score Wood. After a groundout by Crews scored Mead, Lile singled in García, pushing the lead to 10-1.

The Giants began their rally in the eighth. Chapman led off with his second home run, a solo shot to center. Rafael Devers followed with another solo home run. Jung Hoo Lee walked, Bryce Eldridge walked, and Daniel Susac doubled in Lee. Drew Gilbert grounded out to score Eldridge, and after a strikeout, Casey Schmitt flew out to end the inning, but the Giants had cut the deficit to 10-6.

Washington added a run in the top of the ninth when Mead homered to left-center, his 10th of the season, giving the Nationals an 11-6 lead. But the Giants’ comeback was far from over.

In the bottom of the ninth, Luis Arraez led off with a double to right. Chapman doubled to score Arraez, making it 11-7. Devers walked, and Lee singled to load the bases with no outs. Eldridge then crushed a 1-0 pitch to right field for a grand slam that tied the game at 11 and sent the crowd of 32,459 into a frenzy. The Giants had erased a five-run deficit in the inning and completed the improbable victory.

Mitchell Parker took the loss for Washington, allowing five runs — four earned — on five hits over one inning of relief. He fell to 2-3 on the season. Reiver Sanmartin earned the win with two innings of relief, allowing one run on two hits while striking out two. Sanmartin improved to 1-0.

Daylen Lile had a standout day for Washington, going 4 for 5 with two RBIs. Curtis Mead added two hits, including a home run. James Wood also homered and drove in two runs. For San Francisco, Chapman’s four-hit performance was the highlight, but Eldridge’s grand slam proved the decisive blow.

The game lasted 3 hours, 2 minutes.

Washington had won the first two games of the series, 6-3 on Tuesday and 4-3 on Monday, but the Giants avoided the sweep with Wednesday’s dramatic victory.

The Nationals now return home for a six-game homestand beginning Friday against Seattle. The Giants will host the Chicago Cubs for a three-game series starting Friday.

Interstat’s game simulator had projected a final score of Washington 5, San Francisco 4. Interstat’s ELO system gave San Francisco a 55.60 percent probability to win. Washington was installed as a pregame favorite with a spread of minus-1.5. The total score of 21 went under the over-under line of 8.5.