OAKLAND, Calif. -- Jeremy Giambi thinks it's going to be a little weird for everyone when his big brother mans first base at the Coliseum wearing a gray Yankees uniform rather than green and gold.

In his six years with the Oakland Athletics, Jason Giambi became a fixture both on the field and in the clubhouse. With tattooed biceps, a Hollywood smile and a powerful bat, he was the A's model player.

But tonight he'll return to Oakland with the team that has won four of the last six World Series and knocked the A's out of the playoffs for two straight years.

"The fans here will probably boo him when he appears. It's their right. They paid for their tickets and they can do anything they want," Jeremy said. "But I think they should respect him for what he did, he gave the team here a lot of great years.

"It would probably be different if he wasn't a Yankee now. That team is always the team to beat for any team to get to the playoffs."

Jason, known for his eternal optimism with the A's, expects a mixed reaction.

"There's going to be people who are happy to see me. The nice thing is there are Yankees fans all over the world," he said. "There will be people who are disappointed. It will be real emotional, for sure."

Could have stayed

The A's could have kept their All-Star first baseman, the 2000 AL MVP, for $91 million over six years. But Oakland refused to give Jason the no-trade clause he wanted.

So Jason accepted a $120 million, seven-year contract with the Yankees in December, leaving behind the team that gave him his start.

A lot has changed since he bolted.

Jeremy, an outfielder, has taken over his big brother's locker. Third baseman Eric Chavez has assumed the slugger role with seven home runs, and young Carlos Pena has been posted at first base.

Jason, meanwhile, has had to adjust to living and working under much more scrutiny than he ever faced in Oakland. He is batting .263 with four home runs and has been booed at times by the demanding New York crowds.

An MVP runner-up last season after hitting .342 with 38 homers and 120 RBIs for Oakland, Jason also led the league in on-base percentage (.477) and slugging (.660) last season.

He joined a team that has not had a 30-home run hitter in 10 of the last 14 seasons.

Jeremy said he thinks his brother is trying too hard.

"I just think he's trying to show what he can do every game instead of trying to relax up there," Jeremy said. "He wants to make everyone happy."

While Jason faces the realities of being a Yankee, his little brother is finding a groove with the Athletics. Jeremy is off to arguably the best start of his career, batting .353 with 24 hits and four homers.

"He's happy that I'm having a good year," Jeremy said. "He's my biggest fan and I'm his."