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KANSAS CITY, Mo. -- Brian Bannister felt fine warming up in the bullpen. On the field, something just wasn't right and he was in a jam right off the bat.

Once he worked out the kinks, the right-hander was as good as he's been all season.

Bannister worked six scoreless innings to outpitch Jarrod Washburn and the Kansas City Royals extended their winning streak to six games with a 3-1 victory over the Seattle Mariners on Thursday.

Bannister was in trouble right away, laboring through a 27-pitch first inning. Facing runners on the corners with one out, he struck out Russell Branyan and got Adrian Beltre to line out, setting up one of his best outings of the season.

"I just made some pitches when I had to," Bannister said. "Getting through that inning knowing I didn't have my best location really helped me the rest of the game."

The Royals turned four double plays in front of 32,714 screeching fans -- it was School Day at The K -- and overcame some shaky moments from closer Joakim Soria to earn their eighth win in nine games overall. They have won six straight against Seattle for the first time since 1989 and swept a home series against two teams for the first time since 2003.

The Mariners have lost four straight and eight of 11 overall thanks to a failing offense. Ichiro Suzuki had three hits and Ken Griffey Jr. had a pair. The rest of the Mariners weren't so good, combining for four hits and 11 strikeouts.

Seattle, the AL's third-worst scoring team, has just eight runs in its last four games. It has scored one run or less in eight games this season.

"It's a shame -- Washburn pitched well," Mariners manager Don Wakamatsu said.

A day after pounding out 17 hits in a 9-1 win over the Mariners, the Royals managed just seven hits and had to scrap for all of their runs.

That's all they needed the way Bannister (3-0) was pitching.

He settled in after the shaky start, finishing with seven strikeouts, getting out of jams with double-play balls in the second, fourth and sixth innings. Bannister allowed five hits and walked one in his fourth start since being called up from Triple-A Omaha on April 21.

"I would put that right up there with one of the top three starts that we've seen this season," Royals manager Trey Hillman said.

Ron Mahay and Juan Cruz each threw a scoreless inning before Soria made it interesting in his first outing since Sunday.

Kansas City's closer, who's been bothered by a sore shoulder, gave up two hits, including Mike Sweeney's run-scoring single, and walked two to load the bases with two outs. With the Kauffman Stadium crowd getting antsy, Soria finally closed out his seventh save by getting Ichiro to bounce into a fielder's choice.

"Everybody is so used him coming in and doing it on nine or 10 pitches and 1-2-3," Hillman said. "It was just rust."

Washburn (3-2) was nearly as good as Bannister.

The left-hander, coming off a solid outing against Oakland on Saturday, pitched effectively through seven innings, allowing two runs and six hits.

The Royals got an unearned run off him in the third inning when shortstop Ronny Cedeno bobbled David DeJesus' routine grounder for an error. Kansas City added another in the fifth on Willie Bloomquist's single -- extending his hitting streak to 10 games -- a sacrifice and Mike Aviles' run-scoring single up the middle.

But that was it off Washburn. Kansas City's only other run came in the eighth, when Billy Butler made it 3-0 with a run-scoring single off Sean White.

"I feel good with how I pitched," said Washburn, who has allowed two runs or less in five of six starts. "I didn't have good stuff today. My sinker was very good today and that pitch was enough to get me through."

Game notes

Royals second baseman Alberto Callaspo, seventh in the AL with a .359 average, was given the day off. ... Mariners play-by-play man Dave Niehaus, who started with Seattle's first season in 1977, worked his 5,000 game. ... Ichiro made a nice sliding catch on Mike Jacobs' sinking flyball to right in the fourth inning.