Boston Red Sox’s Xander Bogaerts celebrates his two-run home run in the first inning of the team’s baseball game against the Tampa Bay Rays at Fenway Park, Thursday, Aug. 1, 2019, in Boston. (AP Photo/Elise Amendola)

BOSTON — The Red Sox stood pat during Wednesday’s trade deadline, and then the Tampa Bay Rays gave Boston perhaps its most crushing loss yet during a disappointing World Series defense.

Rookie left-hander Brendan McKay struck out seven, Mike Zunino and Austin Meadows homered, and the Rays beat the Red Sox 9-4 Thursday night to complete a three-game sweep.

“It’s tough to win here. Period,” Rays manager Kevin Cash said. “It’s tough to win a series here, let alone do what we just accomplished. We should feel good about ourselves.”

Tampa Bay swept a series of at least three games at Fenway Park for just the second time in club history. The Rays have won four straight and hold the AL’s final wild card by a half-game over Oakland.

Boston fell 3 1/2 games behind Tampa Bay. The Red Sox lost their fourth straight and dropped 10 1/2 games back of the AL East-leading Yankees a week after taking three of four against New York in Boston. The Red Sox limp into a four-game weekend series in the Bronx at 59-51, all but out of contention for a fourth straight AL East title.

“I think these were the most disappointing losses of the season,” said Xander Bogaerts, who homered twice while going 4 for 4.

Mookie Betts also homered for the Red Sox, but it wasn’t enough to overcome Tampa Bay’s clutch hitting and Boston’s struggles both offensively and defensively.

“It didn’t look good,” manager Alex Cora. “We’ll talk to them. We’ll address it because that can’t happen. We’ve got to be better.”

Boston was 1 for 11 with runners in scoring position and left seven on base. Andrew Benintendi hit lead-off doubles in the fourth, sixth and eighth innings but never scored.

Red Sox starter Andrew Cashner walked five while allowing seven runs in 5 2/3 innings, and Boston’s pitchers combined for eight walks and two wild pitches.

Tommy Pham had two RBI singles and Jesús Aguilar singled and scored twice in his debut for the Rays, who picked him up from Milwaukee in a trade before Wednesday’s deadline.

“We’ve got a great group here,” Aguilar said. “They’ve been solid for the whole season and I think it’s going to be a fun year for us.”

Eric Sogard, another deadline addition, also had two hits for the Rays.

McKay (2-1) got his second win in the majors, holding Boston to three runs and seven hits in 5 1/3 innings.

FENWAY BLUES

The Rays’ only other sweep at Fenway Park came in April 2010. Tampa Bay improved to 9-6 against the Red Sox this season and won 8 of 9 in Boston.

“You never want that to happen. Fenway Park is supposed to be for us,” first baseman Mitch Moreland said.

OUT OF CONTROL

Cashner (10-6) had a 2-1 lead after Bogaerts’ two-run homer in the first but fell apart quickly in the second. He walked Aguilar to start the inning, Sogard followed with a single and Zunino drew another walk to load the bases. Cashner walked in one run, Tampa Bay added another on a passed ball and Pham hit an RBI double to put the Rays up 4-2.

Cashner ran into more trouble in the sixth when Aguilar singled with one out, Sogard doubled to right and Zunino drew a walk to load the bases. Darwinzon Hernández replaced Cashner and threw a wild pitch that allowed Sogard to score from third and another pitch in the dirt that led to another run and a 7-3 lead for the Rays.

The three-run rally came just after Bogaerts’ second homer of the game pulled Boston within 4-3 in the fifth.

“You’ve got to go out there and shut them down there and I just didn’t do it,” Cashner said.

TRAINER’S ROOM

Rays: Optioned RHP Trevor Richards to Triple-A Durham. Manager Kevin Cash said the Rays want to build up Richards, acquired Wednesday in a trade with Miami, for longer appearances. … Optioned 1B Nate Lowe and RHP José De León to Durham to clear roster spots for Aguilar and RHP Nick Anderson.

Red Sox: C Christian Vázquez (sore right knee) was out of the lineup after taking a wild pitch off his right knee in the seventh inning Wednesday night.

UP NEXT

Rays: After a rare Friday night off, Tampa Bay hosts Miami in a two-game interleague series Saturday and Sunday. The Rays have yet to name a starter for Saturday against Marlins LHP Caleb Smith (7-4, 3.43 ERA).

Red Sox: LHP Eduardo Rodríguez (13-4, 4.13) gets the start Friday night in the opener of a four-game set against the first-place Yankees in New York. Rodríguez tied a career high for victories Saturday when the Red Sox beat the Yankees 9-5.