On Sunday, Ross reiterated that the job is still Chatwood's to lose.
"I think Chat's in a really good place and a head space," Ross said prior to the Cubs 11-9 loss to the Reds. "His outings have been very powerful and he's made a statement, as has Millsy. And he's got some experience that Millsy doesn't have. So, I would still say Chatwood's in the lead for that role, but Millsy's having a great spring."
In Saturday's loss to the Reds at Las Vegas Ballpark, Mills was strong into the fourth inning. The right-hander has given up just one run on four hits (all coming Saturday) in 9 2/3 innings this spring. Chatwood has seven strikeouts and two runs allowed in six spring innings and is slated to start again on Tuesday against the Giants.
A large part of the equation for Ross is Chatwood's Major League experience (192 games vs. 19 for Mills), combined with the righty's solid showing last year. In a swing-man role, Chatwood posted a 3.76 ERA with 74 strikeouts and 37 walks in 76 2/3 innings. He pitched in every inning from the first through the 14th, made five starts, finished nine games, saved a pair and logged 38 outings with varying days of rest.
"I'm never going to put him in a situation that he hasn't already seen," Ross said.
There is such a difference in the respective arsenal's of Mills and Chatwood that it makes sense to debate who should start and who should be in the bullpen. Mills features a fastball that hovers around 90 mph with a changeup, slider and one of the slowest curveballs in MLB. Chatwood sits around 95-96 mph on his fastballs with elite spin on his breaking pitches.
It could be tempting to utilize Chatwood's more overpowering arm as a reliever.
"I've definitely thought about that," Ross said. "That's why I think Tyler is maybe one of the most valuable starters slash long guys that we have, because he can do multiple roles. There's not too many guys we've got coming out of the 'pen that throw 99, which he hit last year, I saw a couple times. He's got power stuff."
When Ross does officially announce his fifth starter, the manager said Mills and Chatwood will remain in the roles they are assigned. Even though it could make sense to mix and match based on opponent, Ross believes it is important for pitchers to establish their routines. Ross also wants to avoid risking injury by shuffling pitchers between roles.
"Whoever wins that fifth job, they earned it," Ross said. "Going back and forth to the 'pen, the arm can get some wear and tear and I just feel like you're asking for injuries."
Souza mans center
Early in camp, Ross made it known that he planned on being cautious when it came to Steven Souza Jr.'s workload. The outfielder missed all of last season while recovering from a devastating left knee injury and the manager wanted to make sure Souza was not being asked to do too much this spring.
More evidence of Souza's incredible progress arrived Sunday, when Ross gave the go-ahead for the outfielder to play center field in the Cubs 8-1 loss to the D-backs in Arizona.
"I've thought he's looked great," Ross said. "He's moved very well. I think the feedback we've gotten from the trainers and how his knee and his whole body has bounced back after some rigorous outings [has been positive]."
• Ross remains publicly undecided on which pitcher will get the nod for the Opening Day starter assignment. Yu Darvish, Jon Lester and Kyle Hendricks each have a case to earn that honor. The manager said an announcement on that front could come during the upcoming week.
• In his second Cactus League appearance of the spring, Cubs closer Craig Kimbrel worked two-thirds of an inning against the D-backs in Arizona. Kimbrel allowed a two-run home run to Jake Lamb and finished with no walks, two strikeouts and three hits surrendered.
• Cubs lefty José Quintana, who projects to be the fourth starter, logged two innings against the D-backs on Sunday. Quintana struck out two, walked two and was charged with one run on three hits.
"You get to the end of the game and you get to see these guys' at-bats, the young guys. And I'm still locked in. I'm just watching, how's this guy going to impact us? And, who do I like? And, how does this guy carry himself? How is he on the field? How's he get down the line? All that. It's really fun. It's just like, 'Man, these are my guys.' It's cool. It's cool to watch." -- Ross, on managing some of the team's prospects in Spring Training games
The Cubs have a team off-day on Monday, but return to Cactus League play with a 2:05 p.m. CT tilt against the Giants on Tuesday in Scottsdale, Ariz., live on MLB.TV. Chatwood will take the mound for Chicago, continuing his push for the lone rotation vacancy.