TUCSON, Ariz. -- The D-backs set their pitching staff on Tuesday with Yusmeiro Petit, Juan Gutierrez, Doug Slaten and Billy Buckner nabbing the final four spots in the bullpen.

Bobby Korecky and Leo Rosales, who had been in the mix, were optioned to Triple-A Reno following Tuesday's game.

The D-backs will open the season with a rotation of Brandon Webb, Dan Haren, Doug Davis and Jon Garland, with would-be fifth starter Max Scherzer set to begin on the disabled list, until a No. 5 guy is needed on April 14.

With Scherzer off the roster to start, the D-backs had four rather than three spots open in the bullpen, which will include Chad Qualls, Tony Pena, Jon Rauch and Scott Schoeneweiss.

Here's a closer look at the four pitchers who claimed spots on Tuesday:

Buckner: The right-hander pitched well in every outing except for one and compiled a 3.31 ERA. He could have been on the outside looking in had there only been one three spots because he does still have Minor League options remaining.

"I've seen a guy that has good stuff and isn't afraid to compete," Arizona manager Bob Melvin said.

A starter by trade, Buckner's curveball has been impressive enough this spring that the staff feels it could be a big weapon for him in the middle innings.

Gutierrez: Posted the worst numbers of any of the competitors with a 8.74 ERA, but was saved by a couple of factors. First, he did pitch well early in camp, which helped offset a string of poor outings at the end.

Secondly, Gutierrez, who was acquired in a trade that sent Jose Valverde to Houston, was out of Minor League options and, with a 95 mph fastball, the team was concerned it would lose him.

"The way Gutierrez pitched early on, maybe not as good lately, but gives us some length on top of that," Melvin said.

Petit: The veteran was a favorite coming into camp based on the fact that he was a solid contributor to the team last year and he, too, was out of Minor League options.

A polished pitcher, Petit does not possess an overpowering fastball, but has excellent command, a good feel for pitching and has proven that he fills that swing role in the bullpen.

Slaten: When camp began, the team hoped Slaten would pitch well enough to make the team and provide another lefty in the 'pen to go with Schoeneweis.

After a rough start to spring, Slaten skipped an appearance and instead worked on the side with pitching coach Bryan Price on lowering his arm angle to three-quarters rather than over the top, and since then he has pitched much better.

"Slater pitched really well especially down the stretch," Melvin said.