The door remained shut until Wednesday, when Hannahan was given his first start of the season in the opener of a two-game set against the visiting Rangers.
"I prepare every day like I'm going to start, anyway," Hannahan said. "You have to take that approach, or at least I do. Whether you start or not, you have to be ready to play."
Garciaparra had been filling in for injured third baseman Eric Chavez, and with Ellis out, it stood to reason that Bobby Crosby and Hannahan, both of whom spent the bulk of last year as regulars, would step into everyday roles.
But despite Hannahan having started a team-high 109 games at third base last season and posting the second-best fielding percentage among American Leaguers at the position, the A's started Crosby at the hot corner in each of the six games after the injuries to Ellis and Garciaparra.
Prior to that, Crosby, the starting shortstop last season, had started all of four games there during his pro career.
Hannahan is also strong at second base, but Eric Patterson (two games) and Gregorio Petit (four) got the starts there after Ellis and Garciaparra went down.
"Jack's an incredible defensive player," said Oakland manager Bob Geren.
Geren wouldn't say it, but Hannahan's offensive struggles last season and this spring likely kept him out of the starting lineup until Wednesday, when Crosby got his third career start at second.
After posting the lowest batting average (.218) among big league regulars in 2008, Hannahan batted .208 without a homer in 26 Spring Training games. He started the season at Triple-A Sacramento and was batting .157 in 13 games when he was called up April 24.
Hannahan, 29, homered in his first at-bat back, but went hitless in his next eight at-bats prior to Wednesday's start.
"Obviously it's nice to hit a home run your first time up; it's nice to hit a home run any time," Hannahan said. "But we're kind of scuffling for runs, and I have to hit if I want to play."
Ironically, Hannahan's glove probably got him into the lineup. Crosby has struggled at third at times and made an error Tuesday that led to two unearned runs in a loss to the Angels.
Geren on Monday suggested that Petit would be the starter at second with Ellis out. Two days later, he'd changed his tune
"Let 'em all compete for playing time," Geren said.
Mychael Urban is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.