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NEW YORK -- Joba Chamberlain walked off the mound in the fourth inning, his head down. After another shaky start, his spot on the New York Yankees' playoff roster could be in jeopardy.

Chamberlain lasted just 3 2/3 innings and was booed by fans at Yankee Stadium during the Kansas City Royals' 4-3 victory Wednesday night, which stopped New York's seven-game winning streak.

"I understand what I've done and the situation I've put myself in," the slumping pitcher said.

Derek Jeter homered leading off the first, and Chamberlain left with a 3-1 deficit before Nick Swisher's 29th homer tied the score in the fifth, a two-run drive off Robinson Tejeda. But the Yankees ended the first regular season at their new $1.5 billion ballpark the same way they began -- with a loss.

Chamberlain allowed three runs, seven hits and four walks, throwing just 52 of 91 pitches for strikes and going to three-ball counts on six of 22 batters.

He gave up a run-scoring single to Brayan Pena in the first, a bad-hop RBI single to Mark Teahen in the third and another run-scoring single to Pena that finished his night in the fourth. It could have been worse: the Royals loaded the bases with one out in the second before Tug Hulett popped out and Billy Butler flied out.

"It was not a good start," Yankees manager Joe Girardi said.

In his first full season as a major league starter, Chamberlain wound up 9-6 with a 4.78 ERA in 31 outings, throwing 156 1/3 innings as the Yankees limited his pitches in the final two months. But he finished poorly, going 1-4 with a 7.75 ERA in his final 10 starts, giving up 56 hits in 40 2/3 innings.

With CC Sabathia, A.J. Burnett and Andy Pettitte set to start in the first round of the playoffs, Chamberlain either will go to the bullpen -- where he excelled in 2007 -- or be dropped from the division series roster.

"He's had a lot of success out of the bullpen," Girardi said. "I can't guarantee that when you put a guy in situation that he's going to revert back to his old form if we do put him in the bullpen, but he does have a lot of confidence coming out of those gates."

Chamberlain blamed his problems on poor fastball command and said the first cool weather of the autumn bothered him. He's willing to accept any postseason role, and he could get a start in later rounds.

"If they want me to fold towels, I'll fold towels," he said. "I don't really care. I'll do anything to win on this team."

New York opened its high-tech stadium on April 16 with a 10-2 defeat against Cleveland but went on to finish 57-24 (.704) at new Yankee Stadium, the third-highest winning percentage since 1901 for a team in a first-year ballpark, according to STATS LLC. The Boston Red Sox were 57-20 (.740) with one tie in 1912 at Fenway Park, and the Boston Somersets were 49-20 (.710) in 1901 at the Huntington Avenue Baseball Grounds.

Yankee Stadium finished with its first season with a major league-leading 237 home runs, tied for the 18th-most during one season at a major league ballpark, STATS LLC said. New York hit 136 home runs at home, matching the eighth-highest total in big league history.

Kansas City, which completes its season this weekend against Minnesota at the Metrodome, broke a seventh-inning tie when Teahen walked against Damaso Marte (1-3) and John Buck tripled off Sergio Mitre on a catchable drive that Swisher got turned around on and then fell down. Yuniesky Betancourt followed with a missed a squeeze bunt, and Buck was tagged out by catcher Jorge Posada.

"It's good to play teams that have something to play for, so it keeps our intensity high," manager Trey Hillman said.

Jamey Wright (3-5) pitched two innings for the win, and Joakim Soria got three outs for his 30th save in 33 chances. After Betancourt's throwing error from shortstop put runners on second and third with two outs in the ninth, Soria retired Ramiro Pena on a flyout to shallow center.

"It's a good win against a really, really, really good team," Wright said. "You want to face the best, and they probably are."

Game notes

Home attendance was an AL-high 3.72 million, down 13 percent from last year's 4.29 million at old Yankee Stadium, which had a bigger capacity. ... New York started all its regulars for the first time since clinching the AL East on Sunday, but began pulling some after the sixth inning. Girardi plans to use his regulars Friday at Tampa Bay when Sabathia goes for his 20th win.