Manager Cecil Cooper cited two main reasons for choosing Ausmus over Towles for the opener at PETCO Park -- comfort and experience.
Cooper wanted his Opening Day starting pitcher, Roy Oswalt, to be as comfortable as possible for the important first contest. Oswalt has a familiarity with Ausmus that he does not yet have with the rookie Towles, and Cooper thought it was best to let Ausmus handle the duties on Opening Day, which always causes a few jitters, even for the most experienced veterans.
Missed playing time during Spring Training was a factor, as well. Towles was out with a hamstring strain for most of the exhibition season, and he spent only three innings catching Oswalt.
"It's not enough time for him," Cooper said. "That's probably more reason than anything else."
The Ausmus-Oswalt pairing doesn't appear to be permanent. Cooper declined to specify how many times he'll play Ausmus when Oswalt pitches, but it's clear he wants his star pitcher and rookie catcher to get familiar with each other sooner rather than later.
At this point, however, Cooper plans to "slowly work in" Towles.
"He'll catch the other guys, for the most part," Cooper said. "He's happy to be here and be a part of this team, and he's our No. 1 catcher. Now, Brad will catch Roy for the time being."
Towles, who entered Monday's game in the seventh inning when Ausmus was lifted for pinch-hitter Darin Erstad, had no qualms about not starting.
"Not at all," he said. "I suspected he might get the start. I know he's more comfortable with Ausmus back there. Anything that's going to help the team is fine. I wasn't disappointed at all."
Ausmus said he thought there was a chance he'd play Monday, but he wasn't sure until he saw the lineup posted upon arriving to the clubhouse.
"There's always excitement surrounding Opening Day, so it'll be fun," Ausmus said. "Part of me feels like J.R. should be experiencing Opening Day too, but I'm assuming he'll be experiencing it in Houston for our home opener [next Monday]."
Alyson Footer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.