Cashner, 24, who was used exclusively in relief as a rookie last season, has been starting this spring and earned the win in his third start on Saturday against the Rangers, a 6-5 Cubs victory. The Cubs' No. 1 pick in the 2008 First-Year Player Draft, Cashner was 2-6 with a 4.80 ERA in 53 relief appearances last year.
In other moves, Jeff Stevens and Casey Coleman were optioned to the Cubs' Triple-A Iowa team. Coleman made a strong case for a spot on the final 25-man roster, but the team feels he needs to get on a regular routine at Triple-A Iowa.
"We decided Cashner will be the fifth starter, and we'll start the season with Mateo as the last bullpen piece," Cubs general manager Jim Hendry said on Saturday. "We felt at this time it was better served for Casey Coleman to continue being a starter -- not that he couldn't be a 'pen guy to help down the road, if he needed to. We felt that [it] was best for his development, and for the Cubs, [for him] to keep developing as a starting pitcher.
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"Mateo had a really good spring," Hendry said. "It was a tough call, but that was really the way we balanced it out. He deserves a chance to be that guy in the 'pen, and Casey would be better served in the rotation."
Silva, 31, was 1-2 with a 10.90 ERA in five spring games and will pitch again on Monday. The Cubs would like the right-hander to go to the Minor Leagues as insurance, but also will listen to offers. He is still owed $11.5 million this season.
Silva, who began last season 8-0 and finished 10-6, had his best outing on Wednesday, when he gave up one run on three hits over six innings in the Cubs' 3-1 win over the Athletics. The one thing the right-hander also had over the other candidates is experience.
"At this time, obviously, we told Carlos Silva that there would not be a spot for him, unless there was an injury between now and Opening Day," Hendry said. "We will try to explore trade possibilities for him with other clubs who might have some interest in taking him right to the big leagues.
"He pitched really well the last outing, [but] he struggled early," Hendry said. "We just felt we wanted Cashner to get the starts and feel good about his future; [we] need to find out where he's at in the rotation plans, moving forward."
This will be the first time Mateo, 26, makes the team's Opening Day roster. The right-hander missed some time this spring to attend his mother's funeral in the Dominican Republic, but posted a 1.29 ERA in seven games in relief.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter@CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.