BOSTON — Boston Red Sox right-hander Matt Barnes threw one pitch too many.

Barnes gave up a three-run homer to Salvador Perez on his final toss, and the Kansas City Royals went on to beat the Red Sox 6-3 Saturday night, ending Boston’s four-game winning streak.

“We felt like at that point and time in that final inning of his work that we wanted him to work through that situation,” Boston interim manager Torey Lovullo said. “He was throwing the ball really well and unfortunately he made a mistake to Perez.”

The homer made it 5-0 and ended Barnes’ second major league start.

Barnes (3-4) gave up five runs and eight hits in 5 1/3 innings.

“Those are situations you kind of learn from,” Barnes said. “Even if the result isn’t what you want, I think you almost learn more from that than if you kind of actually (succeed) every single time. You’re not going to succeed without some struggles first.”

Mookie Betts hit a solo homer, and David Ortiz had two singles and three walks for the Red Sox. Boston had won four of the five meetings with the AL Central leaders this season, and 10 of 12 since the start of 2014.

Yordano Ventura pitched six effective innings, Kendrys Morales added a two-run double and Alex Rios had three singles and an RBI for Kansas City. Following losses the first two nights, the Royals can earn a split of the four-game series Sunday.

Ventura (8-7) gave up one run and six hits, striking out six. He improved to 4-0 in his last six starts. Greg Holland got Travis Shaw to pop out with the bases loaded for final out, earning his 28th save.

Leading 2-0 in the sixth, Perez homered into Boston’s bullpen.

Morales lined his double off the Green Monster in the first inning.

Ventura stranded five runners in the first four innings before Boston scored on Shaw’s groundout in the sixth. Betts homered over the Monster off Ryan Madson in the seventh.

TRAINER’S ROOM

ROYALS: Outfielder Alex Gordon is set to start a rehab assignment with Triple-A Omaha Sunday. He’s been on the disabled list since early July because of a strained groin. … Perez took a foul ball off the mask and was shaken up but stayed in the game.

RED SOX: Brock Holt was in the original lineup but was scratched because of a strained left oblique after batting practice. … Ortiz fouled a ball off his right foot in his first at-bat. … Lovullo said right-hander Rick Porcello (soreness, right triceps) could return on the upcoming road trip after he said he “felt great” at the end of a rehab start Friday for Triple-A Pawtucket.

ANOTHER NICE GRAB

Boston’s Jackie Bradley Jr. made a leaping grab at the wall in right field. On Friday, he made a diving catch in left.