Luhnow, who is already gathering information about possible managerial candidates, said the search for a full-time skipper will be a broad one.
"Once we get past that stage [of gathering information], we'll determine which candidates we want to speak to and there's going to be a lot of factors in that," he said. "There's no reason to wait, so we're going to move as fast as we can. The key objective is finding the best possible manager and best possible staff going forward."
Mills, in the final year of his contract, finished his time in Houston with a 171-274 record that included a club-record 106 losses a year ago. He took over a club that saw most of its key veterans jettisoned in trades the last three years as the Astros stockpiled prospects while rebuilding.
Astros owner Jim Crane said the club decided to make a managerial switch to give itself a head start on other clubs that might be in the market for new managers this offseason.
"As we realized it was more than likely we were going to make a change, we felt it was best to make it early so we could have more time to really analyze new candidates," Crane said.
Crane said the club already has four or five names it would like to interview, and he said he'll be involved in the hiring process closely with team president George Postolos and Luhnow. He'd like to have a candidate in place by Nov. 1 at the latest, but hinted it will move much quicker.
"Certainly, we'd like to get it done sooner rather than later," Crane said. "We'll start the process [Monday] and put a list together. Some of our candidates might not be available because they're working for other teams and we'd have to get permission. We'd like to whittle that down to three or four pretty quickly."
The players weren't informed of Mills' dismissal following Saturday's game, and upon arrival at the ballpark Sunday were introduced to DeFrancesco, though most of the players already know him well.
"You never want someone to lose their job," infielder Brett Wallace said. "We prepared with them all Spring Training and all season long. It's definitely not something you want to happen, but in this business, there's change and people get sent down and people sometimes lose their jobs. We have to try to rally together, and I think that's what we're going to do."
Luhnow said he and owner Jim Crane made the decision a week ago they wouldn't pick up Mills' option for 2013 -- when the team moves to the American League -- and Luhnow told Mills after Saturday's loss he wasn't returning.
In addition to introducing DeFrancesco on Sunday, the Astros also tabbed Minor League hitting coordinator Ty Van Burkleo as interim hitting coach and Dan Radison as interim first base coach. Radison had been a special assistant to Luhnow in charge of player development.
"It made sense to make these changes sooner rather than later, not to have a lame-duck administration, to get some new blood in here and for the opportunity to get these guys in here and change the mix a little bit," Luhnow said. "You can't point to one thing and say there was a reason [Mills was let go]. The mix wasn't working, the chemistry wasn't working, for whatever reason."
DeFrancesco, 49, has 17 years of experience as a Minor League manager, including the last two seasons in Oklahoma City. He has 26 years of experience in baseball as a player, coach or manager and had six first-place finishes in the Pacific Coast League Pacific Southern Division while managing at Sacramento in the Oakland organization.
"There's going to be an effort from these guys every day, a commitment to excellence," DeFrancesco said. "Believe me, I want to be the guy who changes the environment around here. I grew up a winner, I had success in the Minor Leagues and it's time to translate that to the Major League level. I'm sure I'm going to make mistakes, but that's part of baseball."
Luhnow said he hasn't made a list of candidates yet, but DeFrancesco will be given a look.
"Everybody's a candidate right now," Luhnow said. "Certainly, Tony's going to have an opportunity to demonstrate the success he's had at the Minor League level and do that up here. We're not ruling anybody in or anybody out. We're just really excited about the opportunity to start with a clean slate and finish the season with the best staff possible for the Astros going forward."
Radison, who joined the club prior to this season, has more than 30 years of professional experience as a player, Major League coach, Minor League manager and coordinator. Before joining the Astros, he spent the 2010-11 seasons as the first base coach for the Nationals.
Radison was the Cardinals' Minor League hitting coordinator for three seasons (2007-09) and was also a first- and third-base coach for the Cubs from 1995-99 and a first-base coach for the Padres from 1993-94.
Van Burkleo coached in the Major Leagues for four seasons, which included the 2007-08 seasons as Oakland's hitting coach and the 2009-10 seasons as Seattle's bench coach. Prior to his Major League stops, Van Burkleo spent six seasons (2001-06) as the roving hitting instructor for the Los Angeles Angels of Anaheim.
"This is a fresh start for us," Luhnow said. "We've got six weeks left in the season. I think the players are going to be excited about putting out the best effort possible to have the best results we can. Yes, we're young, we're inexperienced. We have a lot of talent on this team ... that is capable of being with us for the long term, and we're excited about the group here."