Hannahan, the primary fill-in for Chavez while he was coming back from back surgery, was in the starting lineup Friday at first base, his first start there since 2006.
Hannahan will be back at third on Sunday because Chavez is playing only two consecutive games there right now.
Hannahan carries four gloves with him -- one for third, one for first, one for second base/shortstop and one for the outfield. He said he must be ready for every game.
"They [the coaches] haven't talked too much about what I'm going to be doing," Hannahan said. "Eric playing third was a no-brainer."
Hannahan is batting .233 with three home runs for the season. But he does have six hits in his last 17 at-bats, including a three-hit game in Thursday's 12-0 loss to Toronto.
"We're looking for a way to keep his bat in the lineup," A's manager Bob Geren said.
Hannahan said he has played around 50 games at first base between the big leagues and the Minors. He worked with Geren on Friday at first base.
"If you can play third base in the big leagues, you can be a good first baseman," Geren said.
The A's are desperate for offense at first base. Daric Barton has seven hits in his past 62 at-bats.
So Hannahan knows he could play himself into extra playing time. Both Hannahan and Barton are left-handed hitters, and with Mike Sweeney being hurt, there is no real platoon opportunity at first base.
"It's another opportunity for me to play," Hannahan said.
And a chance to prove he is ready to play anywhere on the diamond.
"I'm glad Bob shows he has confidence in me at a different position," Hannahan said.
Todd Wills is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.