Boston’s Masataka Yoshida watches his grand slam in the eighth inning Sunday against the Milwaukee Brewers. Jeffrey Phelps/Associated Press

MILWAUKEE — Masataka Yoshida has already made some mechanical adjustments at the plate during his rookie season with the Boston Red Sox after starring for years in Japan.

They certainly paid off Sunday.

Yoshida homered twice during Boston’s nine-run outburst in the eighth inning as Boston rallied to beat the Milwaukee Brewers 12-5. He became the first Red Sox player to go deep twice in one inning since Hall of Fame slugger David Ortiz in August 2008.

“I talked to the hitting coach about my mechanics and hitting form, and I found a better one,” Yoshida said through a translator. “I feel more comfortable right now.”

Yoshida is the fourth rookie in major league history to hit two home runs in an inning and the first since Joe Pepitone for the New York Yankees in 1962, according to ESPN Stats & Info.

Yoshida twice led Japan’s Pacific League in batting before signing a five-year, $90 million deal with the Red Sox. He entered Sunday batting just .213 with one homer in 16 games, but the 29-year-old showed in one inning just what he’s capable of accomplishing.

Justin Turner and Yoshida started the eighth with back-to-back homers off Matt Bush (0-1) that gave the Red Sox a 5-4 lead. Yoshida then capped the inning with a grand slam off Javy Guerra that landed in the second deck of right-field seats.

Yoshida, who finished with six RBI, became the fifth Red Sox player to homer twice in one inning, The others were Ortiz, Nomar Garciaparra (2002), Ellis Burks (1990) and Bill Regan (1928).

“This is a really good, good day for me,” said Yoshida, who improved his average to .231. “Still, we are in the season, the beginning of the season. I’d like to keep preparing, keep playing hard.”

Boston bounced back after blowing an early 3-0 lead to move above .500 and win the weekend series. The Brewers’ loss enabled the Pittsburgh Pirates to overtake them for the NL Central lead.

“It shouldn’t be a surprise by now,” Turner said of the way the Red Sox responded in the eighth. “We’ve seen it all year. It doesn’t matter what the score is. These guys don’t give anything away. They keep fighting and clawing, taking good at-bats. We’re never out of a game.”

Brian Anderson went deep twice for the Brewers. Joey Wiemer singled, doubled and scored two runs.

Wiemer gave Milwaukee a 4-3 lead in the seventh by scoring on a wild pitch from Kaleb Ort (1-0). The Red Sox wasted no time regaining the lead.

Turner led off the eighth by sending an 0-1 pitch over the left-field wall to tie the game. Yoshida followed by ripping a 1-2 curveball over the fence in right.

Bush has allowed four homers in 7 2/3 innings this season. His ERA ballooned to 8.22 after getting charged with four runs in one-third of an inning.

“He got huge outs in the Seattle series for us,” Brewers Manager Craig Counsell said, referring to the Brewers’ three-game sweep that preceded this series. “He had a bad day today.”

Since the Brewers acquired him at last year’s trade deadline, Bush has given up 10 homers in 30 2/3 innings.

Guerra allowed a two-run single to Connor Wong and gave up a bases-loaded walk to Turner later in the eighth before Yoshida delivered his 407-foot slam.

Corbin Burnes pitched for Milwaukee six days after leaving a 7-3 victory at Seattle in the sixth because of a left pectoral strain, though he said it wasn’t bothering him Sunday. He gave up three runs – two earned – in the first two innings but held the Red Sox scoreless for the rest of his five-inning stint.

“It was a really tough week for me,” Burnes said. “Just to be able to go out and perform the way I did was kind of something I’m proud of.”

TRAINER’S ROOM

Red Sox: Catcher Reese McGuire wasn’t in the starting lineup after getting hit on the top of his right hand by a foul tip in the ninth inning of Saturday night’s game, but it appears he avoided serious injury. Boston Manager Alex Cora said before the game that McGuire would be available if needed.

Brewers: Right-hander Adrian Houser threw 69 pitches, struck out two and allowed six hits in 4 2/3 shutout innings during a rehabilitation appearance with Triple-A Nashville as he recovers from a groin injury.