Bill O’Brien inherited a Penn State program rocked by scandal, on the cusp of crippling sanctions, and staring at a murky future.

All he ever really cared about was making the Nittany Lions winners.

O’Brien succeeded against heavy odds, overcoming a lack of scholarships, a bowl ban, and player defections. He leaves the program on stable ground after bolting Happy Valley for the NFL and the Houston Texans.

Penn State planned to act fast to find his successor.

“Our anticipation is that we’ll be counting this in a matter of days rather than weeks,” Penn State athletic director Dave Joyner said Thursday.

O’Brien left the Nittany Lions less than two years after replacing Joe Paterno, returning to the NFL to coach the team with the league’s worst record this season.

Naturally, Joyner said there has been tremendous interest already in the vacancy, which should be more appetizing than in 2012. A former offensive coordinator for the Patriots, O’Brien took on perhaps college football’s toughest job in January 2012, joining a school rattled by the Jerry Sandusky child sex abuse scandal.

“I think it’s a lot more attractive at this point, although we had tremendous interest even in spite of everything two years ago,” Joyner said. “From a scholarship standpoint, we’re going to be very competitive right out of the gate. Watching what’s happened here the last two years, if I was a head coach candidate, would make me very excited.”

Defensive line coach Larry Johnson is interim head coach while the search for a replacement goes on.

“I’m humbled by the confidence that Penn State has bestowed upon me during this critical time for the football program and honored to do my part to help Penn State,” Johnson said.

O’Brien will become the third coach in Texans history, following Dom Capers, who led the team from its expansion season in 2002, and Gary Kubiak. O’Brien was set to be introduced Friday in Houston.

Kubiak took over when Capers was fired after a 2-14 season in 2005. Kubiak went 61-64 and led the Texans to their first two playoff appearances and two AFC South titles before being fired in early December.

Houston was expected to contend for the Super Bowl this season, but instead lost nine games by a touchdown or less to end up 2-14.

“In your lifetime, you only get certain opportunities so many times,” O’Brien told reporters at a Houston airport. “This is a great opportunity to work with an owner like Mr. (Bob) McNair and an organization like the Texans. It is a very exciting time for myself and my family.”

O’Brien was proud of his time at Penn State.

“They gave me my first opportunity to be a head coach, and I’ll always thank them for that,” he said. “They’re great kids at Penn State; lot of great people there.”

O’Brien was the first major defection this week. Third-team All-American wide receiver Allen Robinson decided Thursday to forgo his final year of eligibility and enter the NFL draft.

Robinson set Penn State season records in receptions (97) and yards receiving (1,432) for the second consecutive year. He wrote on Twitter: “It was a honor to wear a penn state uniform for 3 years. I will miss my teammates and coaches, blessed for the opportunity and experience.”

Robinson at least gave the program three years. O’Brien only lasted two.

“I believe that Bill O’Brien came here with the intent to be here for a long haul,” Joyner said.

O’Brien, who helped lead the Patriots to the Super Bowl for the 2011 season, arrived in Happy Valley after apprenticeships coaching at Brown, Georgia Tech, Maryland and Duke, followed by five years as an NFL assistant on Bill Belichick’s staff. He won games and won over players with a stern look on his face.

O’Brien did it all in Paterno’s shadow. Over the course of his 61 years at Penn State, Paterno became not just the face, but the cantankerous soul and benefactor of a school that was transformed from a “cow college” into a top-shelf public university.

Joyner said O’Brien never seemed affected by the Paterno loyalists who were slow to warm to an outsider running the program.

“Bill handled that very well, with grace and style,” he said. “I really believe that he loved it here. From the get-go, he looked at himself as a long-termer. But I think a tremendous opportunity came up for him.”

While some scholarships have been restored, Penn State lacks the full allotment other Big Ten schools — including new members Rutgers and Maryland — have at their disposal.