ST. LOUIS — Visiting Boston came up with a pair of unearned runs in the fifth and took advantage of two more Cardinals misplays in the eighth, coming away with a 6-3 victory Tuesday before a crowd of 41,514 at Busch Stadium.

The Redbirds committed three errors and three Red Sox runs were unearned.

The two-game interleague series wraps up Wednesday.

The Red Sox, who’ve struggled to play consistent ball this season, jumped ahead on a pair of solo home runs. Mookie Betts, the reigning American League player of the week, deposited the third pitch of the game into the left-center field bleachers.

With one out in the second, Boston’s Jackie Bradley Jr. went deep to make it 2-0.

The Cardinals rallied with three in the third. After Kolten Wong led off with a single up the middle. Then, after two failed bunt attempts, Boston lefty Eduardo Rodriguez hit the Redbirds’ Lance Lynn with a 1-2 pitch. Dexter Fowler followed with a run-scoring double to the base of the well in left. After a sacrifice fly to center from Tommy Pham tied it at 2, Matt Carpenter drove in Fowler with the go-ahead run on a sacrifice fly to short left. Boston shortstop Xander Bogaerts made a sliding grab with his back to the infield, spun and nearly got Fowler at the plate.

Boston regained the lead in the fifth, coming up with a pair of unearned runs. After Bradley led off with a walk, third baseman Jedd Gyorko was unable to come up with a sharply hit ball off the bat of Devan Marrero. The runners moved up on a swinging bunt from Rodriguez. The tying run scored on a Betts’ groundout and the go-ahead run scored on a base hit up the middle from Dustin Pedroia.

Boston added to its lead in the eighth. After a one-out hit, Bogaerts stole second when he made an acrobatic slide to elude the tag of shortstop Aledmys Diaz after being picked off by Brett Cecil. The Cardinals challenged the ruling on the field, but it was upheld upon review.

After back-to-back walks to Andrew Benintendi and Mitch Moreland loaded the bases, Cecil was replaced by Miguel Socolovich. Christian Vazquez’s sacrifice fly to center made it 5-3.

Another run scored when left fielder Pham dropped a fly ball near the stands along the third-base line. Pham recovered with a strong throw to the plate for the inning’s final out.

Each team finished the night with six hits. The Cardinals got a run-scoring hit from Fowler, who also came up with a nice running catch before running into the wall. Carpenter and Pham drove in the other Redbird runs.

Bradley paced Boston with two hits, including a solo homer. Betts led off the game with a homer and added a run-scoring groundout. He also had the defensive play of the day, gunning down Carpenter when he tried to stretch a single into the double with two outs in the fifth.

With a two-out single in the fifth, Pedroia drove in what proved to be the game-winning run. Vazquez also had an RBI for Boston.

Rodriguez (2-1) picked up the win, with Lance Lynn (4-2) taking the loss.