Mike Yastrzemski hit a game-tying two-run homer in the ninth inning and Thairo Estrada had the go-ahead single in 10th, and the San Francisco Giants rallied to complete a three-game sweep of the St. Louis Cardinals with an 8-5 victory.

Yastrzemski’s shot, which came on a 2-2 count with two outs in the ninth inning off Cardinals closer Giovanny Gallegos, made it 5-5. The Cardinals extended their skid to five games and fell to a season-worst 15 games under .500. It was the third blown save of the season for Gallegos.

Estrada’s single scored Yastrzemski, who was the automatic runner at second base. Wilmer Flores and LaMonte Wade Jr. followed with RBI singles off Steven Matz (0-7).

Tommy Edman’s second career grand slam gave the Cardinals a 4-2 lead in the second inning and Jordan Walker added an RBI single in the third as St. Louis chased Giants starter Anthony DeSclafani after just three innings.

But the San Francisco bullpen shut the door from there as five relievers combined for seven scoreless innings. Tyler Rogers (1-4) got the win with a perfect ninth inning and Camilo Doval earned his 18th save in 19 opportunities.

Cardinals starter Jordan Montgomery gave up three runs in 6 1/3 innings, allowed seven hits, walked two and struck out seven.

Highly touted rookie Luis Matos made his debut for the Giants in center and singled in his first major league at-bat as part of a two-run first inning. Estrada and Patrick Bailey had RBI singles during the rally.

Yastrzemski ended Montgomery’s day with an RBI single in the seventh to make it 5-3 and start the Giants rally.

Miles Mikolas (4-3, 4.02 ERA) kicks off a three-game series on Friday night at New York against the Mets. Mikolas is 1-1 with a 1.64 ERA in four career appearances (three starts) against the Mets.