Giants 4, Cardinals 2: Pinch hitter Brandon Belt’s two-run double in the seventh inning broke open a tie game as San Francisco avoided a three-game road sweep against St. Louis.

Buster Posey went 4-for-4 and scored a run on Hunter Pence’s RBI double in the fourth in support of Chad Gaudin (1-1), who made his first start since 2009. The 30-year-old right-hander threw 55 of his 79 pitches for strikes over six innings, allowing two runs and four hits while fanning five.

Tyler Lyons (2-1) had his first rough outing in three career major-league starts, giving up four runs and eight hits in 6 1/3 innings.

Gregor Blanco’s double-play grounder got San Francisco on the board in the second, matching the amount of runs the Giants scored in dropping both ends of Saturday’s doubleheader. Pence’s double off the wall in center in the third pushed the lead to 2-0 before David Freese evened it in the fourth with a two-run shot.

Lyons allowed a single and walk before departing in favor of Randy Choate, who gave up Belt’s key hit. Jeremy Affeldt relieved Gaudin and tossed 1 2/3 innings while Sergio Romo got the final four outs of the game for his 15th save.

GAME NOTEBOOK: St. Louis C Yadier Molina and manager Mike Matheny were ejected by first base umpire Clint Fagan at the end of the third after Molina slammed his helmet after grounding out with two runners on. Molina appeared to be disgusted with himself, but had to be restrained by Cardinals coaches after he discovered he had been ejected. …. Posey recorded his sixth career four-hit game. … St. Louis hasn’t swept San Francisco at home since 1962.