DETROIT - First baseman Sean Casey is staying with the AL champion Detroit Tigers, agreeing to a $4 million, one-year contract Thursday.

Acquired from Pittsburgh last season, Casey was a hitting star in the World Series. He batted .529 with two home runs and five RBIs against the St. Louis Cardinals, but Detroit lost in five games.

“Everybody is a piece to the winning team,” Casey said on a conference call, “and I felt like not winning last year, but getting there — having that taste of what it would be like to win the whole thing — for me it felt a little like unfinished business.”

Casey also hit .353 against the New York Yankees in the first round of the playoffs. He missed most of the AL championship series against Oakland with a calf injury, but said he’s been healthy since.

“I’m 100 percent,” Casey said. “I felt 100 percent during the World Series.”

Always an enthusiastic and popular player, the 32-year-old Casey batted .245 with five homers and 30 RBIs in 53 games with the Tigers last season. He also has played for Cleveland and Cincinnati.

“Sean did a good job after joining the club, and he was tremendous during the World Series,” Tigers president and general manager Dave Dombrowski said. “We’re happy to have Sean back and look forward to having him for an entire season.

“A true professional, he brings a solid left-handed bat to our lineup.”

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Last week, Detroit acquired right-handed slugger Gary Sheffield from the Yankees for three pitching prospects. Casey said that deal helped make it more appealing for him to return to the Tigers.

“I almost felt that when they signed Gary that it was a perfect fit for me to come back to Detroit,” Casey said.