PEORIA, Ariz. -- D-backs reliever Billy Buckner strengthened his case for a roster spot on Sunday with an impressive two-inning performance against the Mariners.

Buckner allowed one hit and struck out one in his third appearance of the spring, and he has now given up two runs in six innings.

Buckner was originally scheduled to pitch on Friday against Team Mexico in Hermosillo, but a stomach virus that hit him that day pushed his outing back to Sunday.

"It was really good to get back out there and face hitters," Buckner said. "The first inning I felt a lot better. Sitting in the dugout in between innings when we scored a couple of runs, I felt a little winded, but the second inning, I felt fine once I got going again."

The D-backs have three spots open in the bullpen, with at least one of them likely to go to someone who can serve as a long reliever, a role that Buckner could easily fill.

Whether a rotation spot is up for grabs depends on the health of Max Scherzer and Doug Davis.

"That's not my call," Buckner said when asked about his chances of making the team. "I'll do whatever the manager wants me to do. Hopefully I'm right in the mix of things. I'm approaching it that way. Every day I try to come in and get a little better."

With that in mind, Buckner is working on incorporating a cut fastball into his repertoire to go along with a fastball, curve and change. He's thrown it in bullpen sessions, but not in a game yet.

In addition, his inability to finish off hitters has frustrated him.

"I need to do a better job with two strikes," Buckner said. "It seems like I'm getting two strikes a lot and I'm not able to put guys away and they work their way back to a hitter's count, so I've got to work on my two-strike approach a little bit."