Now, naturally, they must adjust to the loss of their top assistant coach.
Wade Phillips, who's turned the Houston defense into the NFL's best, will have surgery this week to resolve a kidney condition and will be away from the team for a week to 10 days.
The 64-year-old Phillips disclosed the medical issue after working with the team at practice on Wednesday. He would not specify the condition, but said it is not life-threatening, is not cancer, and that doctors recommended that he have the procedure.
"I feel good," Phillips said. "I don't have any physical problems right now, so if I get this done, this procedure that I'm doing, then I'll be fine."
Linebackers coach Reggie Herring will run the defense for Houston (10-3) in Sunday's game against Carolina (4-9). Herring was Phillips' linebackers coach in Dallas from 2008-10, then joined Houston's staff after Phillips was hired last January.
"He's ready to do it," Houston coach Gary Kubiak said. "Reggie's called defenses before. We got a lot of confidence. We just need to keep going."
The Texans play at Indianapolis on Dec. 22, and Phillips is hoping to return in time for the regular-season finale against Tennessee on Jan. 1. In the meantime, Herring won't change anything.
"At the end of the day I'm not Wade Phillips," Herring said, "but it's Wade Phillips' system. It's our calls. It's what the players know."
Phillips' leave is just the latest roadblock for the Texans.
Outside linebacker Mario Williams (torn chest muscle) and quarterbacks Matt Schaub (right foot injury) and Matt Leinart (broken left collarbone) are all out for the season, and star receiver Andre Johnson has a strained left hamstring after missing six games with an injury to his right hamstring.
Starting right guard Mike Brisiel had surgery on his broken right leg on Monday, and Johnson only jogged during Wednesday's practice.
Somehow, the Texans have managed to win a franchise-record seven straight games and clinch the AFC South for the team's first postseason berth.
Still, the latest helping of bad luck has everyone in the locker room shaking their heads in disbelief.
"The 'next man up' theme is hitting us everywhere," said two-time Pro Bowl linebacker DeMeco Ryans.
And Phillips has probably made as a big an impact as anyone the Texans acquired this offseason.
Fired as the coach of the Dallas Cowboys in the middle of last season, Phillips talked earlier this season about feeling rejuvenated in Houston, where he played in college and began his coaching career. He took over the league's 30th-ranked 2010 defense, implemented a 3-4 alignment, moved Williams to outside linebacker and the transformation was swift.
Houston now leads the league in total defense at 275 yards per game, ranks fourth in rushing defense at 91.5 yards per game and third in pass defense at 183.5 yards per game. The Texans have held each of their last seven opponents below 20 points.
Linebacker Brian Cushing is one of the players having a breakout year under Phillips' tutelage, leading the team with 86 tackles. He also has two interceptions and three sacks, regaining his form from 2009, when he was named the Associated Press Defensive Rookie of the Year.
"He's been the clear-cut leader of this defense, someone we're obviously going to miss," Cushing said. "But we're not going to try to skip a beat without him. We're going to continue to do what he's taught us, and it'll very, very similar."
Phillips has clearly found a new home in Houston under coach Gary Kubiak. He ran the defense in Denver from 1989-92, overlapping Kubiak's playing career as John Elway's backup for the Broncos, but their history goes back even further.
Phillips and Kubiak first met in the late 1970s, when Kubiak was a ball boy and Wade was an assistant for the Houston Oilers, who were coached by Wade's father, Bum.
Kubiak said Phillips' situation was personal to him.
"The most important thing is Wade's health right now," Kubiak said. "He needs to go get this done and the doctors feel very good about it. He needs to take care of his health and we need to take care of the football for him."
The biggest change for the Texans may be adjusting to Herring's fiery personality. While Phillips is calm and soft-spoken during practice, Herring is often working up a sweat and barking orders.
"Reggie's a lot more of a vocal guy," Ryans said. "Everybody's under his control now, so I don't know if he has that much yelling in him."
Herring, a defensive coordinator at some of his previous college stops, says he's ready to take on the added responsibility.
"I feel very confident about this," he said. "We're all in a good frame of mind right now. We have a lot of things to finish, home-field advantage. We have a lot to play for right now.
"Players have shown a lot of character and pride," he said. "I don't see any letdown in these guys. At the end of the day, Wade will be with us every snap. This is his system, his defense and we'll move on."