Arizona manager A.J. Hinch said Wednesday that it was no secret Billy Buckner had a leg up in his battle for a spot in the rotation. So assuming Buckner is the No. 4 guy, that leaves Rodrigo Lopez and Kevin Mulvey to battle for the fifth and final spot.
Both pitched Thursday against the A's at Phoenix Municipal Stadium.
Lopez started and allowed one hit over three shutout innings. He was so efficient with his pitches, throwing just 31, that he had to go to the bullpen after the outing to get the rest of his work in.
"Every time I go out there, I feel better as far as command and balance on the mound," said Lopez, a non-roster invitee.
Since allowing three runs in a two-inning stint on the first day of Cactus League play, Lopez has put together eight scoreless innings.
"Rodrigo was great," Hinch said. "He had all his pitches. He was very impressive today with all of his pitches and with how efficient he was. He showed some promise today in how he can attack a Major League lineup."
Mulvey pitched later in the game, and his line was not as impressive -- four runs on five hits in 2 1/3 innings in suffering the loss.
In fairness, the four runs were unearned, as the D-backs played sloppy defense behind him in the sixth.
"I thought Mulvey threw the ball well today, too," Hinch said. "He was the victim of unstable play, some that resulted in errors and others that were plays that should have been made. We made him get about five outs in two of his three innings, and that wasn't his fault. He was up in the zone a little bit, and he started to feel for his pitches."
Regardless of whether Lopez or Mulvey win the job, it's still likely the fifth starter would open the year in the Minors, given that the D-backs do not need a No. 5 starter until April 17. By beginning the year with its fifth starter in Triple-A, Arizona could keep an extra arm in the bullpen.
"We really could go a lot of different ways," Hinch said. "The depth that we have and the choices we have ahead are tough ones."
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.