After watching the left-hander walk 13 over his past two starts, D-backs manager A.J. Hinch said Wednesday that the team will use Willis as a reliever beginning Friday.
"It's worth a shot," Hinch said. "We've got to get the walks under control. That's the motivation behind getting him to the bullpen, put him in a little better position to be successful and match him up a little easier."
By matchups, Hinch is referring to using Willis primarily against left-handed hitters. The D-backs do not have a lefty in their bullpen at the moment.
"I think it will be good for me," Willis said. "I feel it will help me get myself right and get my arm slot where I want it to be. I totally agree with A.J. on the move. I like it. The less I think, the less I think about messing it up, so I think it might be a good thing for me. I've had chances to do it."
Right-handers are hitting .322 against Willis this year, while he has held lefties to a .188 mark. If he is able to carry that success against lefties into the 'pen, it would be a help in the National League West, where teams have left-handed middle-of-the-order hitters like Adrian Gonzalez (Padres), Andre Ethier (Dodgers), Brad Hawpe (Rockies) and James Loney (Dodgers).
"There's going to be some good situations for me to help the team out, that's the good thing about it," Willis said. "San Diego has a couple of good lefties [and] L.A. has a couple of good lefties in the middle of the lineup, so I think it's going to pay dividends for our team."
The D-backs acquired Willis from the Tigers earlier this month in exchange for Minor League right-hander Billy Buckner.
Willis was unable to get out of the fifth inning of his Tuesday start and walked six in the 8-0 loss to the Cards.
"I did feel a lot more comfortable with my mechanics yesterday," Willis said. "I just didn't get the results like I wanted to, but I did feel really comfortable repeating my mechanics. I can't continue to walk guys and expect to win. You've got to put somebody in there that can throw strikes."
Barry Enright, who made his Major League debut Wednesday, is expected to remain in the rotation in place of Willis.