Jalen Beeks pitched four strong innings against the team that traded him last month and the Tampa Bay Rays limited Boston to two singles, beating the Red Sox 2-0 on Sunday.
Joey Wendle and C.J. Cron homered as the Rays topped the AL East leaders for just the fifth time in 16 games this season. Six of those Tampa Bay losses have been by one run.
Boston, which owns the majors' best record, lost for only the fourth in 21 games and was shut out for the fifth time this season.
Beeks (2-1) gave up one hit in relief, striking out three and walking two. The 25-year-old left-hander was acquired from the Red Sox before the trade deadline for pitcher Nathan Eovaldi.
Sergio Romo worked pitched the ninth for his 16th save and 100th of his career. Reliever Diego Castillo started for the Rays, getting five outs. It was the club's 34th time to have a reliever start, and was Castillo's first major league start.
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Boston starter Hector Velazquez (7-1) gave up a run and three hits in four innings. He took Chris Sale's turn in the rotation a day after the ace lefty was put on the 10-day disabled list for the second time in nearly three weeks with mild shoulder inflammation.
Wendle hit his homer into Boston's bullpen in the second. Cron hit his 24th off a billboard above the Green Monster seats in the ninth.
Boston's best chance came with two on and no outs in the fourth, but MLB RBI leader J.D. Martinez bounced into a double play.
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Martinez went 0 for 3, snapping his streak of reaching base successfully in home games at 51 straight, the third-longest string in club history. Ted Williams owns the record with 69 in 1941 and Joe Foy is next with 54 in 1966.
Red Sox RF Mookie Betts made a charging, diving catch of Cron's liner in the fourth and 3B Eduardo Nunez made a sliding stop to his left on Tommy Pham's grounder before throwing him out.
Rays: C Jesus Sucre returned to the lineup after missing the previous four games with a sore right wrist.
Red Sox: LHP Eduardo Rodriguez (10-day DL, sprained right ankle) is slated to have a rehab start for Double-A Portland on Monday. . Knuckleballer Steven Wright (DL, left knee inflammation since late June) is expected to pitch a live batting practice this week.
Rays: RHP Ryne Stanek (1-3, 2.74 ERA) is slated to start the opener of a four-game series Monday at home against Kansas City RHP Jorge Lopez (0-2, 4.44).
Red Sox: RHP Rick Porcello (15-5, 4.04) is set to face Cleveland ace Corey Kluber (15-6, 2.68) when the AL Central leaders come to Fenway Park Monday for the opener of a four-game series.