These days, though, they are competing for the Cardinals' fifth starter spot. The loser will end up in the bullpen or back at Triple-A Memphis.
Kelly allowed three hits and one run in four solid innings and Miller allowed three runs in 2 2/3 innings Thursday in St. Louis' 5-4 win over the Atlanta Braves.
With the Cardinals wanting the three remaining spring training starts to go to the No. 5 starter, Thursday was likely the final opportunity for the candidates to show why they deserve the spot.
"Oh definitely, if he gets the fifth spot I'm not going to talk to him anymore," Miller said. "I'm kidding. It's not going to change anything. I'll be happy for him, but I'm sure if I got it he'll be just as happy for me."
Kelly has allowed just five hits and two earned runs in eight innings over three starts.
The former third-round draft pick by the Cardinals in 2009 got two double plays in his four innings and the only damage came on a two-out single from Braves leadoff man Jordan Schafer in the third that scored Jordan Parraz.
Miller allowed six hits and three runs but two of them scored after he departed the game.
"Joe came out and I thought that was probably the best he's been this spring," said manager Mike Matheny. "Shelby threw the ball pretty well, as well. It was a good day.
"Today wasn't a drop dead, have to make a decision day, but we just took in more information and gave them another opportunity to go out there and I thought they both did the most with it," Matheny added.
Mike Minor allowed six hits and four runs in five innings for the Braves and retired 12 of the first 14 hitters he faced. But he tired in the fifth inning as the Cardinals batted around and scored four runs on five hits off the lefty.
"We've got to get him through those innings to build up pitch count and that kind of stuff," said Braves manager Fredi Gonzalez. "Other than that, he did a lot of good things. He helped himself with a bunt, drove a guy in. He did a lot of good stuff."
Young outfielder Jordan Parraz went 4 for 4 and had two runs scored for the Braves, who tied it 4-all in the seventh inning before Matt Adams' two-out single put the Cardinals back in front for good in the bottom of the eighth.
Kelly stepped into the big league rotation last summer when Jaime Garcia went down with an injury and went 5-7 with a 3.53 ERA in 24 appearances -- 16 starts -- after making his Major League debut on June 10.
He became a valuable weapon in the Cardinals bullpen last October, giving up just two earned runs and six hits in 7 2/3 innings but would seem to be headed back to the starting rotation after another positive outing Thursday.
"We've messed around a couple times but no hatred towards anybody," Kelly said. "We're best friends. It is what it is. We're not trying to hide from each other or anything. We live together, too. We converse with everything we do.
"Me and Shelby, we don't ask anything. We just go out there and pitch when we're supposed to pitch," he added. "We both pitched today and lined up on the same day. I don't know (what happens) from there honestly."
Miller wasn't promoted to the big leagues until September but had a 1.32 ERA in six appearances and took a no-hitter into the sixth inning in his first career start on the final day of the regular season. He made two appearances in the NL championship series.
The right-hander got a late start this spring training due to a small bout with shoulder soreness. He's yielded six runs and ten hits in 7 2/3 innings for a 7.04 ERA. But the right-hander was pleased with how he pitched Thursday and with what he's done to show the Cardinals he can pitch at the big league level.
"I feel like I've been throwing well," Miller said. "I definitely have been throwing better than probably what my numbers look like. I feel good and I felt like my fastball is definitely a lot better than it was last year but at the same time, Joe has been throwing just as bit.
"It's really not up to me. I feel like there's always room where I could have proved that I was more ready," he said. "There's always something and we're both working on things but at the end of the day Mike's going to do what's best for the team and whatever happens, happens."
Matt Holliday returned to the Cardinals lineup after missing nearly a week with the flu. . Matheny said shortstop Rafael Furcal's Tommy John surgery went well Wednesday. The surgery was performed by Dr. James Andrews. ... Cardinals outfield prospect Oscar Taveras went 2 for 4 and is hitting .302 this spring. . The Braves optioned David Hale after Wednesday night's game in Jupiter.