"I really want to [name the rotation] by Sunday, yes," Maddon said. "We'll tell them tomorrow or at the end of the day Sunday."
With staff ace Scott Kazmir coming back slowly from a strained left elbow, James Shields is the Opening Day starter and Matt Garza will fill the No. 2 slot, leaving five pitchers to compete for the remaining three spots in the rotation.
Sonnanstine delivered a shining performance in the Rays' 2-1 loss to the Yankees on Friday, allowing no runs on three hits, two walks and two strikeouts over five innings and lowering his spring ERA to 0.64 in six games. Of the 63 pitches he threw on Friday, 43 were for strikes.
"Sonnanstine looked really good," Maddon said. "Had all of his pitches working and made pitches when he had to -- a very, very impressive performance.
"Sonnie's a pro. He comes ready every day. A lot of lefties in that lineup today, he pitched very well against the lefties today. Yes, he made a very good case for himself."
Also in contention for spots in the rotation are: Edwin Jackson (0-1, 5.40 ERA in four games), Jeff Niemann (2-0, 1.50 in four games), Jason Hammel, (0-1, 7.13 in five games) and J.P. Howell (1-0, 1.00 in in five games).
"Felt like I showcased what I have pretty well, attacking hitters," Sonnanstine said. "I'm very happy with the way I performed tonight and set myself up for a possible spot."
Sonnanstine had one of his best starts of the 2007 season against the Yankees in New York on Aug. 31, when he allowed one run on two hits over eight innings to pick up the win.
"It's a tough lineup, that's for sure," Sonnanstine said. "But after that game in New York, that win, that was a huge confidence booster for me. You know, I know it can be done. So I just have to try and think like that every time I face them."
While Sonnanstine seemed to separate himself from the pack on Friday night, his spring has been anything but easy.
"Definitely. There's been a lot of what ifs, but those decisions aren't up to me," Sonnanstine said. "So I just have to roll with the punches, be glad I'm coming to big league Spring Training."
Maddon was not specific about what would be the determining factors for selecting his starters, but it likely will be a combination of what they've done in the past combined with what they have done this spring.
Possibly swaying the decision is the fact that Jackson and Hammel are each out of options, so neither can be sent back to the Minor Leagues without clearing waivers. Also coming into play is who in the group can pitch in relief. Currently, Sonnanstine, Howell and Hammel all appear as possibilities to go to the bullpen, while the Rays will want Niemann to start in St. Petersburg or Triple-A Durham.
"It's still competitive in a sense," Maddon said. "I think we pretty much know what we want to do, but we want to wait a couple of more days to decide upon it."
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.