Pete Alonso, Coby Mayo go deep as Orioles beat Red Sox 4-2 at Fenway

One of the players the Red Sox heavily pursued in free agency proved to be the difference Tuesday night.

Pete Alonso, who was linked to Boston throughout the offseason before signing a lucrative deal with the Orioles, delivered the decisive blow in Baltimore’s 4-2 win at Fenway Park.

With the game tied in the third inning, Alonso launched a go-ahead two-run homer into the Green Monster seats. The blast, his 12th of the season, traveled 400 feet and left the bat at 110.8 mph.

Alonso’s swing ultimately provided the margin in a game the Red Sox struggled to recover from offensively.

The loss dropped Boston to 25-34 on the season and 9-20 at Fenway Park, its worst home start since 1932.

Connelly Early turned in another solid effort despite taking the loss. The rookie left-hander worked 6 1/3 innings in his 12th start of the season, allowing four earned runs on six hits while striking out six and walking one.

The Orioles did most of their damage via the long ball, tagging Early for a pair of home runs, including Alonso’s game-changing shot in the third inning.

“Today, I just felt like he was behind the count too often, even when he got ahead in the count they did a really effective job, fouling off, fouling off, fouling off,” interim manager Chad Tracy said of his starter. “There was just a lot of pitches in the first few meetings, especially, they grinded him out. … I’m sure he’ll tell you, (it) wasn’t his best.

“That being said, he got us an out in the sixth, which did not look feasible as we were about halfway through the third. It is important that he got through where he did, and we were able to not overextend our bullpen.”

Early threw 96 pitches (64 for strikes), including 49 pitches over the first two frames. Coby Mayo quickly erased the 1-0 lead the Red Sox took on Jarren Duran’s leadoff triple and Wilyer Abreu’s RBI sacrifice fly, with a high fly that was changed from a double to a Green Monster homer in the top of the second.

Duran started June strong after hitting .347 (17 for 49) with six home runs over his final 11 games in May. Duran connected for a leadoff triple on a knuckle curve from Shane Baz.

“I think they did a very good job with their plan, and I didn’t execute in a lot of counts, so (they) took advantage of that,” Early said.

After keeping the ball in the park through his first eight career starts, Early has run into trouble with the long ball. The left-hander has now allowed 11 home runs in his last nine outings after giving up none in his first eight starts, including Game 3 of the Wild Card Series last fall.

“Yeah, (I’ve) given up a lot of home runs, so still trying to figure that one out,” Early said.

Early has been noticeably better away from Fenway Park this season, mirroring a trend that has affected the Red Sox as a whole. The rookie owns a 2.67 ERA across six road starts, spanning 33 2/3 innings. Tuesday marked his sixth home start, and after allowing four runs to Baltimore, his ERA at Fenway climbed to 3.85 over 32 2/3 innings.

“I think we did a really good job in this past series on all sides of the ball,” Early said, “and then to lose the momentum that we have built over the past couple games is tough.”

Boston’s offense continued its frustrating boom-or-bust trend, going 0-for-3 with runners in scoring position while leaving four men on base.

Meanwhile, Baz carved through the Red Sox lineup over seven strong innings. The former Rays starter allowed two runs on four hits, walked two and struck out six while throwing 94 pitches, 64 for strikes.

The loss dropped Boston to 18-27 against right-handed starters this season.

After surrendering Duran’s leadoff triple in the first inning, Baz retired 12 of the next 13 batters he faced. The lone exception was a two-out walk to Willson Contreras in the opening frame.

The Red Sox scratched across their second run in the fifth when Mickey Gasper led off with a single and eventually scored on Marcelo Mayer’s sacrifice fly.

That was about all the damage Boston could muster.

Baz stranded Caleb Durbin after a one-out double off the Green Monster in the fifth and worked around Ceddanne Rafaela’s leadoff single in the sixth. In the seventh, he erased a leadoff walk to Gasper by inducing an inning-ending double play off the bat of Isiah Kiner-Falefa.

By the time Baz exited, he had largely neutralized a Red Sox lineup that continues to struggle to generate consistent offense.

“We took care of the opportunities we had,” Tracy said of the pair of RBI sac flies. “That was the two real chances we had. We executed both those spots, but we just didn’t give ourselves enough other opportunities.”

Greg Weissert didn’t have to navigate any inherited runners when he replaced Early and took advantage, tossing 1 2/3 scoreless innings to keep Boston within striking distance.

Rookie left-hander Tyler Samaniego followed with a high-wire act in the eighth.

Gunnar Henderson appeared to beat out a ground ball to first base, but the Orioles challenged after Samaniego was ruled to have reached the bag first. The call stood following review.

Adley Rutschman then drew a walk and Alonso followed with a single, putting two runners aboard. But the Orioles ran themselves out of the inning when Samuel Basallo’s ground-ball single struck Alonso as he attempted to advance to second, resulting in an unassisted out. Samaniego needed just one more pitch to escape, getting Mayo to pop out to Contreras.

The left-hander worked around a one-out single by Leody Taveras in a much quieter ninth inning.

Combined, Early, Weissert and Samaniego held Baltimore scoreless over the final six innings.

Contreras appeared to strike out leading off the ninth, but successfully used an ABS challenge to overturn what would have been strike three from Rico Garcia. The reprieve was short-lived, as Contreras swung through the very next pitch for the first out.

Masataka Yoshida followed with a strikeout and Gasper lifted a routine fly ball to end the game, handing the Red Sox their 20th home loss of the season.

The Red Sox and Orioles continue their three-game series Wednesday night at Fenway Park. Rookie left-hander Payton Tolle (2-2, 2.61 ERA) is scheduled to start for Boston opposite Orioles right-hander Chris Bassitt (4-3, 5.06 ERA).