SEATTLE — Whit Merrifield crushed a pair of homers, the Royals’ bats churned out six runs against lefty Yusei Kikuchi and Homer Bailey cruised for 7 2/3 innings as the Royals raced past the Mariners, 9-0, on Tuesday at T-Mobile Park.

Kansas City is now riding a season-high-tying three-game win streak; the other came during a three-game sweep over the Indians at Kauffman Stadium in April. Tuesday’s win also clinched the Royals’ first road series win of the season.

Bailey gave the Royals’ relievers much-needed length after the bullpen pitched 9 1/3 innings over its previous two games. Bailey also pitched back-to-back scoreless outings for just the third time in his career, and for the first time since 2013, when he was at his peak with the Reds.

“I think he pitched fantastic. We were short in the ‘pen,” Royals manager Ned Yost said. “It was just a great job by him. He gave the bullpen the breather that they needed.”

After shutting out the Tigers over six innings of two-hit ball in last Thursday’s 7-3 win in Omaha, Bailey struck out six on Tuesday and allowed just five hits and two walks, both to Daniel Vogelbach. From the second inning on, Seattle tallied just two hits against Bailey, who tossed 121 pitches, tied for the second-most of his career, a highmark he hadn’t reached since 2014.

On Tuesday, through a tailored gameplan with catcher Martin Maldonado and pitching coach Cal Eldred, Bailey neutralized the Mariners’ lefty-heavy lineup by jamming their hitters up and in with an effective mix of his slider, splitter and four-seam fastball, which reached 95 mph.

“They’ve got some lefties who we just kind of felt like going in it’d be good for us to work off the split, maybe try to get a few strikes on some curveballs,” Bailey said. “The preparation that Maldy and Cal had too was so good, too, and that really helped me a lot.”

Bailey credited his improved command from the third inning on — when he retired 14 of his final 16 batters, with just two hits after the second — but he also pointed to a critical inning-ending double play in the second by Merrifield at first base that helped halt a potential Mariners rally. Merrifield made a quick reactionary snag of a 94.5 mph line drive by Mac Williamson.

Merrifield started at first for the third straight game as part of a matchup plan with left-handed-hitting Lucas Duda as the only other first baseman on the roster. It was just his 10th career start at first, though he is widely considered among the game’s most versatile players, having logged Major League innings at every position but catcher and shortstop.

But Merrifield doesn’t even own a first-base mitt, he said. For now, he’s borrowing Cheslor Cuthbert’s. However, with shortstop Adalberto Mondesi expected to miss Wednesday’s series finale with right groin tightness, Merrifield will likely move back to second base.

“The offense will fluctuate, but I’ve always felt like my defense should be good year-round,” Merrifield said. “I shouldn’t go into defensive slumps, in my opinion. So when my offense is good, the whole game is going right for me. I was told at a young age that defense doesn’t slump, and I’ve tried to carry that throughout the course of my career.”

At the plate, Merrifield had his second multi-homer game of his four-year career (his first was on July 23, 2017, against the White Sox), and in the process, he compiled a career-high six RBIs.

Merrifield has been particularly exceptional in Seattle, where he’s now 14-for-36 over eight career games. He’s now hit safely in 20 of 23 career games against the Mariners, and his 31 hits against them are his second-most against any team outside of the AL Central. Merrifield also extended his hitting streak to eight games. He now has 10 homers this season, including eight on the road, and two shy his career high set last season.

“I think I’m taking better advantage on the road,” Merrifield said. “We play at the biggest park in the league. You’re not going to hit a lot of homers at our park. That’s just the reality of it. Guys put up big homers at other parks, and that’s not the reality of our park.

“My swing is feeling good. I’m putting the barrel on the ball, and when I do, I can put up some numbers.”