Red Sox right fielder Kevin Pillar falls on his back after hitting the wall while making a catch on a ball hit by Ryan Mountcastle of the Orioles during the fifth inning Saturday in Baltimore. Julio Cortez/Associated Press

BALTIMORE — Pedro Severino singled in the winning run in the 10th inning to punctuate a poor performance by Boston’s revamped bullpen Saturday night, and the Baltimore Orioles beat the Red Sox 5-4 to snap a six-game losing streak.

Coming off a lackluster performance against the Yankees in which he allowed three runs in three innings, Red Sox starter Martin Pérez gave up five hits over seven innings and left with a 3-1 lead.

That left it up to Boston’s new-look bullpen to seal the victory. One night earlier, the rebuilding Red Sox traded veteran relievers Heath Hembree and Brandon Workman to Philadelphia for a pair of young starters.

So Josh Taylor entered with his 16.20 ERA to start the eighth inning. He got two quick outs before issuing a walk, and Anthony Santander followed with a game-tying homer inside the left-field foul pole.

Boston used three straight walks off Cole Sulser in the 10th to regain the lead, but in the bottom half, Matt Barnes (1-2) let in the tying run on a wild pitch before Severino hit a liner to left-center with the bases loaded and one out.

Miguel Castro (1-0) got the final two outs in the 10th to help the Orioles end Boston’s modest three-game winning streak.

Jackie Bradley Jr. homered and Alex Verdugo had two doubles and an RBI for the last-place Red Sox.

Pat Valaika put Baltimore ahead 1-0 in the second with his fifth home run, the most he’s had in a season since hitting 13 with Colorado in 2017.

Boston went ahead 2-1 in the fifth. Bradley sent a 2-1 pitch over the wall in center – his first homer of the year – before José Peraza and Verdugo hit back-to-back doubles.

Kevin Pillar drove in a run in the sixth with an infield hit.

Orioles starter Alex Cobb gave up two runs and six hits over five innings in another frustrating outing at Camden Yards. Since joining the Orioles in March 2018, the right-hander is 0-9 in 16 starts at home.

FIRST HITS

Orioles prospect Ryan Mountcastle got his first big league hit on a dribbler down the third-base line in the ninth inning. In addition, teammate Ramón Urías celebrated his first major league start with a third-inning single for his first hit.

ROSTER MOVES

Red Sox: Boston recalled left-hander Jeffrey Springs and right-hander Robert Stock to fill out the bullpen. The two pitchers obtained in Friday’s trade, Nick Pivetta and Connor Seabold, were optioned to the team’s alternate site.

Orioles: Outfielder Dwight Smith Jr. was designated for assignment and the team selected the contract of outfielder Mason Williams from its alternate site. Williams “offers more versatility in the outfield,” according to Manager Brandon Hyde, which is important with center fielder Austin Hays (rib fracture) on the injured list. “Selfishly, we hope he will remain in the organization after this designation period,” GM Mike Elias said of Smith. “Great kid, great player.”

TRAINER’S ROOM

Red Sox: Manager Ron Roenicke said outfielder Andrew Benintendi (rib cage strain) “is certainly doing better” but was unsure if X-rays had been taken recently. Benintendi has been on the IL since Aug. 12.

Orioles: Chris Davis (knee) will be assessed on a week-to-week basis, Elias said, insisting there is no inclination at this time to shut down the slumping first baseman (.122, 1 RBI) for the season. … Reliever Hunter Harvey (right forearm strain) is throwing to batters at the alternate site. “If everything progresses well, I think you’ll see him by the end of the month,” Hyde said.