MINNEAPOLIS -- Yusei Kikuchi pitched much better on Thursday for the Mariners. The bullpen, however? That was another story, as the Twins jumped on Seattle after Kikuchi’s departure and rolled to a 10-5 series-clinching win at Target Field.

After getting roughed up in his last three starts, Kikuchi looked much sharper while allowing just one run on six hits over five innings against the American League’s top-scoring team. The 27-year-old rookie from Japan at least quieted some questions after going 0-3 with a 14.40 ERA and lasting just 3 1/3 innings in each of his previous three games.

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“These last three games haven’t been very strong, so I just wanted to go out there and do whatever I could for the team,” Kikuchi said through interpreter Justin Novak. “It does build confidence for me.”

But the Mariners couldn’t cover up their bullpen issues, which remain one of the major reasons the club has lost 41 of its last 57 games in falling to 29-43. Rookie Brandon Brennan gave up four runs without recording an out after replacing Kikuchi as the Twins jumped on three relievers for six runs in the sixth.

Minnesota took two of three in the series while improving to 45-22, solidly atop the AL Central, and wound up 5-2 against Seattle for the season.

Kikuchi (3-4, 4.78 ERA) worked his way in and out of trouble in the second, loading the bases with no outs and then escaping by striking out Jason Castro on a 95-mph fastball and Byron Buxton with an 89-mph slider and then inducing AL-batting leader Jorge Polanco into a ground out.

Kikuchi also got a double-play grounder from Marwin Gonzalez in the first to negate an error on rookie Shed Long, who mishandled the first ball hit to him in his first MLB start at third base.

The free-agent signing of Kikuchi was one of the Mariners' major offseason moves as they piece things together for the future, so his return to form was welcome.

“It was great to see Yusei get on top of his game,” said manager Scott Servais. “I thought he threw the ball really well against a good-hitting team. He had a really good slider today and got the fastball where he needed to. That’s what we’d seen from Yusei, so it was nice to see that coming back … There were a lot of positive signs. Getting him back on track is going to be really key for us moving forward.”

Kikuchi said he got some good advice from the Mariners pitching coaches over the past week and leaned more on an elevated fastball as well as sharper secondary offerings.

“I feel like my slider was really good,” Kikuchi said. “If you look at my velo with that, I was 82-83 with that pitch the last three games and today it was up to 90, so I felt that was something to hit on.

“Those games were personally pretty hard for me, but as my career goes on, I feel like going through that will really help me in the long run. All my teammates have been saving me. It was a great outing for me today.”

The Twins finally got to Kikuchi in the third with a line-drive homer by former Mariner Nelson Cruz, who wound up going 3-for-4 with three RBIs on the day. Kikuchi turned a 1-1 tie over to his ‘pen after Daniel Vogelbach ripped a run-scoring single in the top of the sixth and had the Mariners in good shape until the Twins teed off late.

A rough run for Brennan

The Mariners’ Rule 5 Draft pick Brandon Brennan was outstanding for the first two months of the season, posting a 2.05 ERA with 29 strikeouts and 12 walks while allowing a .176 opponents’ batting average in his first 21 outings and establishing himself as a versatile late-inning option.

But with veterans Hunter Strickland, Chasen Bradford, Sam Tuivailala and now Connor Sadzeck on the injured list and Anthony Swarzak, Shawn Armstrong and Nick Rumbelow traded or released in recent weeks, the Mariners relief crew has been through tremendous turnover and Brennan has carried a large load.

The big right-hander hasn’t been the same in his last nine appearances, with a 17.61 ERA on 15 runs, 11 hits and eight walks with six strikeouts in 7 2/3 frames, and he underwent some medical tests postgame due to growing concern with fatigue in his back and right shoulder while throwing.

“It’s becoming more work,” Brennan said. “Usually it’s free and easy, like the beginning of the year when you’re fresh. I don’t know if it’s just different because I haven’t had this big of a work load coming from the Minor Leagues. I’m trying to adjust to the game up here, so it’s probably more fatigue than anything.”

The 27-year-old didn’t record an out while giving up a hit, two walks and a fielder’s choice grounder that scored a run when Dee Gordon’s throw to the plate was too late to catch a sliding Ehire Adrianza. Brennan also committed a throwing error on a pickoff attempt and unleashed a wild pitch.