But with the Astros' front office wheeling and dealing over the past few weeks, Mills' task over the final two months of the season is clear: help his younger, inexperienced players establish themselves in the Majors.
In Mills' mind, the key for younger players looking to stay at the top level of professional baseball is making adjustments on a regular basis.
"If a guy comes with that attitude of wanting to learn and knowing that he has to make those adjustments, because we can tell them as much as we want and take them to the video and show them in here, but sometimes guys just have to go through it, especially if they haven't struggled in the past," Mills said.
The Astros picked up their first road win since July 16 on Saturday. With another victory on Sunday, they can take the three-game weekend series against the Braves at Turner Field.
The Braves, 15-7 since the All-Star break, will look to Kris Medlen in their effort to top the Astros. The right-hander has made 19 career starts, but only one in 2012: on Tuesday against the Marlins. He went five innings, giving up one run on four hits for the win.
"I was so much more calm," Medlen said after the start. "If you would have asked me before my first start in 2010 or before the first start of my career, it would have been completely different. But I just felt like I was in control and I was trying to pound the zone. I knew I had a pitch count, but I wasn't too worried about it."
Medlen will make at least two more starts before Tommy Hanson returns from the disabled list sometime after Aug. 15. For now, the Braves are keeping their options open with Medlen, a middle reliever for most of this season.
"My career, I've taken it a day at a time, and every day it has been different," Medlen said after his start. "The fact that I get another start is good for me and I'm happy about it."
Against the Astros on April 10, Medlen gave up two runs in 1 1/3 innings in relief.
Braves: Astros in AL will be odd for Jones
The Astros' move to the American League after this season doesn't make most of the younger Braves emotional. But third baseman Chipper Jones, a prominent figure in the teams' rivalry in the late 1990s and early 2000s, said Houston's departure from the National League will be "very strange."
The Braves knocked the Astros out of the postseason in 1997, '99 and 2001. The Astros returned the favor in '04 and '05.
"They were our rivals," Jones said. "We had some great battles when they had the Killer B's. I really enjoyed going up against them and I always liked going to Houston."
Sunday marks the conclusion of the Astros' final trip to Atlanta as members of the NL.
Astros: Norris on the mound
A season that started so well for Bud Norris, the Astros' starter on Sunday, has taken a wrong turn since the middle of May.
After posting a 3.14 ERA in his first nine starts, Norris' ERA in his last 10 starts is 7.10. He carried a shutout into the seventh inning of his last start, but gave up three runs in his final inning and took a no-decision.
"I'm trying to get out there and win, because I'm a competitor," Norris said after the start. "I know these guys are playing hard behind me."
The right-hander is riding a career-long seven-game losing streak. He hasn't earned a victory since May 21.
Second baseman Jose Altuve's hitting streak ended at seven games on Saturday after an 0-for-1 night at the plate. Altuve had a career-high three walks.
With two homers on Saturday, outfielder Justin Maxwell became the fourth Astro with a multi-homer game this season, and the second in the last four days. Matt Downs and Chris Johnson accomplished the feat earlier this season, and Brett Wallace hit two homers on Wednesday in Milwaukee. Maxwell went 4-for-4 on Saturday.
The only inning in which the Astros have outscored their opponents this season is the eighth. Houston has scored 59 runs in the eighth inning and has allowed 56.
After Saturday's 3-2 loss, the Braves are 4-30 when scoring two or fewer runs.