In a move swift to the point of blindsiding the man pegged to be his replacement and shocking to the pitching staff, the Astros fired pitching coach Brad Arnsberg Tuesday — a stunning fall for someone who was credited with much of the Astros staff’s improvement in 2010.

Doug Brocail was pulled off the trade-deadline preparation he was doing in his former role as special assistant to the general manager to take over on an interim basis.

After several weeks of mounting tensions and what the club described as “philosophical differences,” things came to a boiling point in a disagreement in Monday’s series finale against the Braves. Manager Brad Mills and general manager Ed Wade spoke by phone after the game, and Wade called Arnsberg on Tuesday morning to inform him he had been fired.

“We couldn’t seem to get on the same page. Brad Arnsberg is a tremendous pitching coach, has a great work ethic and a tremendous passion for what he does and the guys that he worked with,” said Wade, who flew back to Houston from a personal trip, speaking to the suddenness of the change. “But when differences of opinion become philosophical differences, then something has to be done about it.”

Added Mills: “To do something like this is tough. But at the same time, we’re trying to do what we can and create an atmosphere for these guys to be successful.”

Arnsberg felt the atmosphere had been deteriorating for weeks.

Job became ‘less fun’

“It got less and less fun to come to the ballpark, and that’s not good,” Arnsberg said, citing disagreements with Mills and Wade. (All parties declined to get into specifics.)

The move was so sudden that Brocail, a 15-year major league veteran, said he had not been given the time to brief his wife before accepting. Brocail said he would have that conversation late Tuesday, but he could see himself finishing the year as pitching coach.

Arnsberg’s firing comes 20 months after he was hired following a stint in Toronto to replace Dewey Robinson, who was gone in the purge of much of Cecil Cooper’s coaching staff.

After a slow start last year, Arnsberg’s staff finished in the middle of the National League pack, with particular improvements from Bud Norris and Wandy Rodriguez, both of whom have continued their success in 2011.

The rest of the staff, for the most part, has plummeted. At the time of Arnsberg’s firing, the Astros stood second-to-last in the National League with a 4.69 ERA and had a major league-worst 13 blown saves in 23 chances.

The firing was not performance-related, it was stressed, nor was it part of a larger housecleaning by the incoming ownership group. In fact, because Arnsberg signed a contract extension last September and there was more than a season and a half left on the deal, the current brass reached out to owner-to-be Jim Crane regarding the move.

So Arnsberg, who will receive the money he is due on his contract, packed up his truck and headed to the Metroplex, where he keeps his permanent home. He spent much of Tuesday morning speaking with the pitchers he is leaving behind and said those relationships were never strained.

“I think there were philosophical differences between the skipper and myself and Ed and myself,” Arnsberg said. “I’ll leave here, for whatever it’s worth, with my head held extremely high, and I wish (owner) Drayton (McLane) and the players, coaches and front-office people nothing but the finest.”

Among those whom Arnsberg aided most was Brett Myers, who credited the coach with helping revitalize his career. Arnsberg was a big reason Myers signed a midseason extension last year instead of testing the free-agent market.

Players, staff offer praise

“He was very strong-minded and believed what he believed in, just the way I am,” Myers said. “It’s kind of hard not to butt heads with a guy when we think we’re right most of the time. Sometimes it doesn’t work, and sometimes it does.

“It’s just tough to see a guy who has a mind like that and understands baseball as much as he does … to get rid of what I thought was one of our assets. But that’s not our decision.”

That was the feeling around the clubhouse and one echoed by Brocail, who last pitched in the majors with the Astros in 2009.

“I’m taking over for one of the best pitching coaches in the game,” said Brocail, who will try to be a fast learner and who, like Arnsberg, will emphasize video work as part of preparation. “I sat the guys down to say, ‘Hey, I’m not here to make changes.’ We’re going to go out, get our work in, and hopefully be successful.”

zachary.levine@chron.com