Left-hander Yusei Kikuchi had a game he would like to forget. Home runs proved costly as the Mariners lost to the Red Sox, 6-5, at Fenway Park on Friday night.

Kikuchi, who lasted 4 2/3 innings, had one easy inning, and that was in the fourth. The trouble started in the first. Seattle was up, 1-0, following a Kyle Seager double, but the Red Sox quickly took the lead in the bottom of the inning on a two-run homer by Xander Bogaerts.

“I don’t know how I hit it out, but I was definitely not looking for [the slider]. For some reason, it ran into my bat path,” Bogaerts said.

Two innings later, Kikuchi was burned by the long ball once again when J.D. Martinez hit a ball over the short fence in right field to give Boston a 3-1 lead.

“Regarding those two home runs, they were hit by their power guys. They were both sliders that caught too much of the plate,” Kikuchi said.

It looked like Kikuchi was settling down after that homer, as he retired the next five hitters.

But Kikuchi lost his touch in the fifth, loading the bases after three batters. Martinez hit into a double play, scoring Bobby Dalbec, before Bogaerts bested Kikuchi again with a single to center field to score Enrique Hernández. Kikuchi said he had problems with his offspeed pitches that inning.

“Kikuchi wasn’t quite on his game [the way] you saw earlier in the season,” Mariners manager Scott Servais said. “He wasn’t quite as aggressive coming out of the chute in the first inning. He hung in there. He battled. He gave us [almost] five innings.”

In his next start, Kikuchi knows what he has to do to keep the Mariners in the game.

“I’m looking to go deep into the ballgame, [and] get outs in key situations, which I wasn’t able to do today,” Kikuchi said.

It was a night on which Kikuchi had to be perfect on the mound because the Mariners’ offense showed once again that it can be a weak link. Entering the ninth inning, they were 3-for-11 with runners in scoring position. Two of those hits came in the first inning. Seattle made it a game when Seager hit a three-run homer off closer Matt Barnes, but Bogaerts snagged an Evan White liner to end the threat.

“We had a ton of traffic out there,” Servais said. “We had nine hits and six walks. We liked what we had going on offensively. Our guys continued to play near the end, but we were a little short tonight.”

Seager snapped a 2-for-33 slump by going 2-for 5 with four RBIs on Friday.

“It’s good to get him going,” Servais said about Seager. “When Kyle is going, our offense really does click. He had some really good swings tonight. It’s a good sign as we move into the weekend, especially this series.”