Sure, part of that has to do with the new 3-4 scheme, but players and coaches alike noticed a different feel to the unit.
Some call it confidence, others say it's swagger, but however it's termed, coach Gary Kubiak says it comes from the group knowing everyone can make plays.
Kubiak also believes the trust the players have in new defensive coordinator Wade Phillips has made a difference in their play.
"They've got a lot of confidence in the guy making the call when it's third-and-5, that's sending the defense in," Kubiak said. "Overall, it's just real upbeat right now and feeling good out of Week 1 and moving on to Week 2."
Houston ranked 30th in the NFL in yards allowed last season with 377 and the 267.5 yards passing a game the Texans yielded was most in the league. The Texans face Miami on Sunday after allowing the fifth-fewest yards in the NFL last week.
Linebacker DeMeco Ryans loves the 3-4 scheme Phillips implemented when he was hired by the Texans in January after being fired as the head coach in Dallas when the Cowboys started 1-7.
"I think the mindset is everyone is just eager to do good," Ryans said. "Everyone wants to be great in this defense, and this defense allows us to be more aggressive. Guys know what to do and how to do it, which allows us to play fast."
The unit is focused on pressuring the quarterback, after ranking 23rd in sacks last season with 30. The Texans excelled at that task against the Colts, sacking Kerry Collins three times, which led to two fumbles.
Mario Williams, the top overall draft pick in 2006, moved from defensive end to outside linebacker this season and had two sacks against Indianapolis.
Phillips was impressed with Williams' debut at linebacker and is sure he wasn't alone.
"I think everybody in the country is, everybody that saw the game and all of our fans and certainly the coaches are," he said. "The guy was a dominant player in the game and that's what we're looking for from him."
Linebacker Brian Cushing thinks the push up front was the key in Houston's improvement.
"I think the pressure's obviously been a lot better, which has helped overall," Cushing said. "I think any time you have a better pass rush and can get after the quarterback, it helps your overall defense, so that's really benefited us so far."
The Texans were encouraged by Cushing's performance against the Colts, when he led the team with seven tackles. He had 133 tackles as a rookie in 2009, but finished with just 76 last year when he served a four-game suspension for testing positive for a banned substance.
He seems to have finally recovered from offseason knee surgery that kept him off the practice field for much of camp.
"He looks really good," Kubiak said. "He's playing very, very hard. The effort he played with last week, if he plays like that all year he's going to lead a lot of things."
Phillips said he doesn't do anything special to build confidence in his players and there's no secret to why his defense is so self-assured already.
"The guys have done a good job of learning their responsibilities and what they're supposed to do and that's part of it," he said. "Then part of it is playing together and playing well. Our first group really played well in preseason and I think that helped our confidence going into the season."
Houston has also been helped by the addition of defensive end J.J. Watt, a first-round draft pick this year, and perhaps more importantly, cornerback Johnathan Joseph and safety Danieal Manning, both picked up in free agency.
The pair is hoping to help turn around the league's worst pass defense from a year ago. Joseph thinks Houston's solid play against the Colts will give the group something to build on.
"I think it rolls over and it carries over, as well as does practice," he said. "If you go out in practice and make plays, it carries over to the game just because it gives you confidence throughout the week that you can do the same thing on Sunday."