Mike Bolsinger allowed two runs on six hits in his MLB debut Monday.

PHOENIX -- In an effort to shake up their struggling starting staff, the D-backs selected the contract of right-hander Mike Bolsinger from Triple-A Reno and optioned right-hander Will Harris to Reno.

Bolsinger, who was 2-0 with a 1.42 ERA in two starts for Reno, made his big league debut by tossing three innings of two-run ball Monday against the Mets in relief of Josh Collmenter, and he will take the rotation spot of Trevor Cahill starting Saturday against the Dodgers in Los Angeles.

Bolsinger, 26, is not overpowering with a fastball in the 88-91-mph range. He throws a cut fastball as his primary pitch and also has a good curveball, while his changeup is still a work in progress.

"I throw a cut fastball like Mariano Rivera," Bolsinger said. "Not as good, obviously -- I wish it could be -- but really that's what I pitch off of and I have a curveball, too, but really I try to establish my fastball and it's been getting a lot of groundouts, so I'm going to keep going with that plan. It's been working in Triple-A. I know this is the big leagues, but just keep going with what's working for you. I'm not going to be the guy that's going to throw 95 past you. I'm going to try and outsmart you on the mound and hit my spots."

Bolsinger was drafted by the D-backs in the 15th round of the 2010 First-Year Player Draft. He was never at the top of any prospect lists, but continued to put together solid outings.

"I've not ever not seen this guy pitch well," D-backs general manager Kevin Towers said, adding that Bolsinger was a strike thrower with "no fear."

One of the biggest improvements that Bolsinger made this year was throwing the ball inside more. That was something he was uncomfortable doing in the past.

"Before the year started, I talked to my dad and I was like, 'I'm just going to kind of let loose this year and blow it all out,' and that's what I've been doing, so hopefully I can keep doing that," Bolsinger said.

Harris had struggled with a 9.72 ERA in seven relief appearances this year and was one of the few relievers that still had Minor League options remaining.

As for those calling for the D-backs to promote top prospect Archie Bradley instead, Towers said that he felt Bradley needed some more time at Triple-A and did not want to cast him in the role of savior for a struggling team.

D-backs move struggling Cahill to bullpen

SF@ARI: Cahill retires Pence to escape the jam

PHOENIX -- Struggling D-backs right-hander Trevor Cahill will have to get his issues worked out in the bullpen.

The D-backs will shift Cahill to the bullpen and replace him with right-hander Mike Bolsinger, who was called up Monday and will make his first start Saturday against the Dodgers in Los Angeles.

Cahill, who allowed seven runs while lasting just four innings Sunday against the Dodgers, has a 9.17 ERA in four starts and has struggled for the better part of the past two seasons.

"Just executing pitches," Cahill said when asked what he needs to do to improve. "It comes down to that. Walks hurt me most of all."

Cahill has walked 13 in 17 2/3 innings this year.

The D-backs desperately would like to get Cahill back on track. They traded away Jarrod Parker for him after the 2011 season and still owe him $7.7 million this year and $12 million in 2015.

The only relief appearance Cahill has made in his big league career came last year when a D-backs game with the Phillies went 18 innings.

"It might take a little pressure off him," D-backs general manager Kevin Towers said. "I think for him, the good thing is he doesn't know when he's going to pitch."

Ross could return to D-backs in near future

Outlook: Ross looking to bounce back from 2013

PHOENIX -- D-backs outfielder Cody Ross could return to action as soon as Friday, when the D-backs take on the Dodgers in Los Angeles.

Ross had Monday off and was scheduled to play back-to-back nine-inning games Tuesday and Wednesday for Triple-A Reno. It would be the first time he has played nine innings on his rehab assignment.

"Everything is feeling good," Ross said.

Ross suffered a fracture and dislocation of his right hip last August, but he has progressed well in his rehab. The D-backs have taken it slowly with him, but they are eager for his return.

"We want him back," D-backs manager Kirk Gibson said. "Trust me."

Arroyo doesn't want to see starters pressing

SF@ARI: Arroyo fans three over 4 1/3 innings

PHOENIX -- With a starting rotation struggling to pitch past the fifth inning, the D-backs' bullpen has been greatly taxed so far in this young season.

The temptation is to say the D-backs need a starter to step up and come up with an outstanding start to turn the tide. That kind of thinking, though, can lead to pressing and then wind up having the opposite effect.

"If you start looking at it like that, it doesn't work when you don't have superstars," veteran starter Bronson Arroyo said.

Using himself as an example, Arroyo said that if you take a look at a two- or three-start stretch from him at any point of a season, it might not look good. But when you look at his end numbers, you'll find 200 innings and a good ERA.

Given the way the rotation is set up, Arroyo thinks it's in each pitcher's best interest to stay within themselves.

"We have a bunch of guys who probably would be No. 3's on a lot of teams," he said. "We probably don't have a lot of two's and one's on the staff and that's the way it is. So we all need to take this season as a marathon, and just be as consistent as we possibly can and let it shake out over the long haul."

Meetings are not the answer. It's simply a matter of each player doing what they can do.

"There's nothing so special that we're missing," Arroyo said. "There's no talks that we're not having, there's no awareness that's not there. It's a matter of going out and playing baseball and trying to consistently do something enough to beat the other club."