Giambi and the A's finalized a $5.25 million, one-year contract with an option Wednesday, bringing the free-agent designated hitter and first baseman back to the place he began his big league career. The sides had reached a preliminary agreement earlier this week but Giambi still needed to complete the obligatory physical for the deal to get done.

FOXSports.com's Ken Rosenthal first reported the preliminary agreement.

Giambi, who turns 38 on Thursday, follows a line of aging and injury-prone designated hitters in recent years with the A's - Frank Thomas, Mike Piazza, Mike Sweeney and then Thomas again. Giambi also could play some first base to give Daric Barton a break from time to time.

After leaving the A's following the 2001 season, Giambi signed a $120 million, seven-year contract with the Yankees. He was slowed by injuries and ensnared in the federal and baseball investigations of performance-enhancing drugs.

New York declined its $22 million option on him after last season, choosing instead to pay him a $5 million buyout.

Giambi thanked the Steinbrenners, Yankees GM Brian Cashman and others in the organization for what he called a "childhood dream" of playing for New York despite the constant media scrutiny and attention.

"When you're with the Yankees, you're like a traveling rock band," Giambi said, noting he's eager to take part in Oakland's rebuilding process and helping to mentor young teammates. "I played with basically 25 superstars in New York every day. They're incredible guys and we had the time of our life."

With Oakland, Giambi gets a $4 million salary this season and the A's hold a $6.5 million option for 2010 with a $1.25 million buyout. He also has a limited no-trade provision and can earn an additional $500,000 each year in performance bonuses: $250,000 each for 525 and 550 plate appearances.

"I'm back here to win," said Giambi, who will join new outfielder Matt Holliday in the middle of the batting order. "I didn't come here just to come back and be the prom queen again and ride through the floats."