KANSAS CITY — Rookie right-hander Brad Keller seemingly was cruising along with a three-run lead and two outs and no one on in the fifth. Suddenly the wheels came off.

Keller gave up four runs in the inning, three on a bases-clearing double by Xander Bogaerts, and the Royals went on to lose to the Red Sox, 15-4, on Saturday night at Kauffman Stadium. Kansas City has lost eight straight and 26 of 30.

Keller’s night came undone when he gave up a single to Mookie Betts, a walk to Andrew Benintendi, and an RBI single to J.D. Martinez. Keller walked Mitch Moreland on four pitches to load the bases. Keller then fell behind Bogaerts, 2-1, and served up a belt-high four-seamer over the middle of the plate — Bogaerts didn’t miss and smashed a bases-clearing drive to the wall in center.

“He was one pitch away [of getting out of the fifth],” Royals manager Ned Yost said. “But that’s a patient team over there. You just kept waiting, but that’s a team … we gave up 10 walks going into the ninth.”

Keller admitted he was just a little off most of the game.

“I definitely didn’t have my best stuff or my best command,” Keller said. “I made some good pitches to get out of some jams, but definitely didn’t have my good stuff.

“I was trying to go on the attack mode [in the fifth]. You get two outs and you just try to stay on the attack, and unfortunately it snowballed on me.

“I made some good pitches that in the past I got swings at, but tonight they didn’t swing at. They’re a disciplined team, a good-hitting team.”

Bogaerts’ double gave the Red Sox a 4-3 lead and chased Keller. The Royals fought back to tie the score, but their bullpen gave up three runs in the seventh — two off Jason Adam.

Lucas Duda gave the Royals a 1-0 lead against David Price in the second with his seventh home run. Duda also was hit by a pitch with the bases loaded in the fifth that tied the score at 4.