Bill O'Brien might not be the coach of the Houston Texans if it weren't for Bill Belichick offering him a low-level job with the New England Patriots after the 2006 season.
What's certain is that mentor nor protégé are going to let any personal feelings cloud the importance of their first meeting as foes Sunday night in Houston.
O'Brien was a quality control assistant in 2007 when the Patriots completed an undefeated regular season before losing in the Super Bowl. New England looked the part again this year by winning its first 10 games but is now on the verge of its first three-game skid since dropping four in a row in 2002 - Tom Brady's first full season as a starter.
Despite spending six years with Belichick and Brady, including one as the offensive coordinator in 2011 before leaving to coach Penn State, O'Brien insists there's nothing from his past that will give the Texans (6-6) an edge.
"That experience with the Patriots was just a great experience for me," O'Brien said. "It taught me a lot about football. It taught me a lot about myself, and I owe a lot to Bill for that.
"I haven't been there in three years and they are a lot different than when I was there."
In fact, the Patriots are a different club than just a few weeks ago. After wide receiver Julian Edelman went down with a broken foot in a win over the New York Giants on Nov. 15, tight end Rob Gronkowski suffered a right knee injury in a 30-24 overtime loss to Denver two weeks later and is out indefinitely.
With Brady's two favorite targets out, he threw a pair of interceptions - one was returned 99 yards for a touchdown - in last week's 35-28 home loss to Philadelphia.
That dealt the Patriots their first back-to-back defeats since 2012.
''We'd love to have everybody healthy. I think everybody would love that,'' said Brady, who also threw three TDs to give him an NFL-high 31. ''It's just not the reality at this point.''
It seemed improbable that the Texans would be in the hunt for the AFC South title following a 2-5 start, but they won four straight before falling 30-21 at Buffalo last week.
Houston had allowed six points three times during its winning streak and gave up fewer than 300 yards in all four, but the Bills busted loose for 390 and hit the go-ahead score on a 40-yard touchdown pass with 1:53 to play.
''It starts with me. We've got to do a better job," said O'Brien, whose team is tied with Indianapolis for the division lead. "But we've got to quickly turn the page.''
He'll employ three former Patriots to help shut down New England's third-ranked offense. Nose tackle Vince Wilfork signed with the Texans in the offseason after 11 seasons with the Patriots, and former linebacker Mike Vrabel coaches the same position with Houston.
Defensive coordinator Romeo Crennel was behind three Super Bowl-winning defenses with New England, but he didn't quite have a player like J.J. Watt on his side.
Watt leads the NFL with 13 1/2 sacks and has a team-high 24 tackles for loss. He was held without a sack for the first time in six games against Buffalo, and Belichick certainly will review film to see how the Bills were able to neutralize him.
The pressure from Watt has helped the Texans rank third in the league in pass defense at 218.3 yards allowed per game.
"I think coach O'Brien has done an outstanding job with the team given where they were," Belichick said. "In spite of all the attention that (Watt) gets and the schemes that are put in from week to week to try to handle him, he still has a tremendous amount of production.
"They move him around a little bit so he's not always in the same place. (It's) similar to what I saw with teams dealing with (Lawrence) Taylor at New York. He's got that kind of disruptiveness."
Brady's former backup will try to navigate the Texans through a New England defense that has forced at least one turnover in every game except one. Brian Hoyer, who was with the Patriots from 2009-11, threw for three touchdowns last week and has a 94.4 rating in nine games.
DeAndre Hopkins caught one of those TDs to set a franchise record with his 10th of the year. He leads the league with 69 first-down receptions.
New England has won five of the six all-time meetings, including the playoffs. Brady has completed 64.6 percent of his passes with 13 touchdowns against the Texans.