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Jason Hammel hopes to put a slight knee ailment behind him this evening when the Baltimore Orioles open a three-game series with the Kansas City Royals at Camden Yards.

Hammel pitched to a 2.09 earned run average through his first six starts, but has allowed eight runs over his last two outings, spanning 10 1/3 innings, while dealing with some pain in his right knee. Regardless, he is 5-1 on the year and a big reason why the Orioles have been one of the biggest surprises in baseball this season.

The 29-year-old righty earned the win on Saturday in Washington, as he allowed four runs and six hits 5 1/3 frames.

"Obviously, I want to be getting deeper into ballgames, but the knee is just not cooperating right now," Hammel said. "I'm doing everything we can between starts to build strength and get to those sixth, seventh, eighth innings."

Hammel is 0-2 with a 7.63 ERA in three career starts against the Royals.

Baltimore enters this weekend series on the heels of dropping two of three to the Boston Red Sox after a 6-5 loss in Wednesday's finale. Jake Arrieta (2-5) gave up four runs on eight hits and three walks through 5 2/3 frames to suffer the loss for the Orioles, who have dropped three of their last four, but still sit atop the American League East with a 28-17 mark.

"It's just a little frustrating to go out there and have that kind of stuff and just not being able to command it early in the game," Arrieta said. "But we were still in a good position. I was still able to get in the sixth and have a shot to even come out in the seventh."

Nick Johnson homered twice and knocked in three runs in a losing effort.

"Got some good pitches over the middle of the plate and put a good swing on them," Johnson said.

Kansas City, meanwhile, also enters on a sour note after losing two of three to the New York Yankees following an 8-3 loss on Wednesday. Billy Butler and Mitch Maier homered for the Royals, who have lost six of eight. In his major- league debut, Will Smith (0-1) was charged with six hits and five runs over 3 1/3 frames.

"The long ball certainly hurt him tonight," said Royals manager Ned Yost. "Some pitches got too much of the plate, but you know it's a tough thing to come in here for your first start against this ball club."

Hoping for a better effort tonight, the Royals will turn to veteran left- hander Bruce Chen, who has won his last three starts after starting the year by losing his initial four decisions.

Chen, who is 2-1 in four starts versus the O's, beat the Arizona Diamondbacks on Saturday, holding them to a pair of runs and eight hits in 6 1/3 frames. He is now 3-4 on the year with a 4.17 ERA.

The Orioles, who swept a two-game series from the Royals last week, are 7-3 this season against left-handers.