The Padres were expected to pick Tim Stauffer to pitch the opener, but he is bothered by a sore right triceps, manager Bud Black said.
Members of the Padres coaching staff have been impressed with the way Volquez has handled the many adjustments they have asked him to make.
"We're still working on being on the same page," Volquez said. "But I think I did well because I did everything they wanted me to do this spring and look what I got now, opening day. I'm going to keep working."
Volquez was 5-7 with a 5.71 ERA in 20 starts for the Reds last season. The right-hander, a 17-game winner and NL All-Star in 2008, was Cincinnati's 2011 Opening Day starter.
"Overall, he's taken very well to the instruction we think is going to help his pitching," Black said. "He's adapted well to the clubhouse. Up and beyond all that, he has thrown the ball well and is deserving of an Opening Day nod."
Black said Stauffer will be pushed back to the fifth spot in the rotation, which means he won't start until at least a week from Tuesday. Stauffer said no one specific area is bothering him but he has noticed "dead-arm symptoms" in his last two outings. Stauffer allowed six earned runs in five innings against the Milwaukee Brewers on Saturday.
"It's unfortunate, but the biggest thing is getting healthy and ready for the season," Stauffer said. "I expect that to be the case. As the trainers say it's probably a little dead-arm symptoms and just need to rest it and heal."