Mercilus, playing in the final year of a $26 million deal he signed in 2015, entered the season playing like a guy not just hungry for a new deal, but hungry to prove people wrong.
Mercilus began the season with sacks in four straight games, compiling five sacks along the way as the defense held opponents to fewer than 20 points per game during that stretch.
"Whitney plays hard. He does a lot of things well," O'Brien said. “He plays the run well, he's instinctive, he rushes the passer well, he does whatever the team needs. He's a good guy to have on the team.”
Mercilus played in more of a limited and complimentary role last season, playing around 75 percent of the snaps, compared to this season where he's been a hard guy to peel off the field, averaging over 90 percent of the defensive snaps per game.
In a larger role this season, Mercilus posted career highs in interceptions (2), as well as forced fumbles (4) and had his third highest sack total (7.5) of his career, tying his output for the 2016 season.
Jonathan Joseph, who has been with Mercilus since 2012, said Mercilus is well-deserving of his new deal.
"He's one of the first guys in the building, last guy to leave, he's always doing extra work," Joseph said. "He'll play any position you put him at, anytime you have a guy like that it's only right that you reward him, because he earned it."
As Mercilus and the Texans get ready for the Buffalo Bills for round one of the playoffs this Saturday at NRG, he's glad he won't have questions about his future in the back of his mind as he prepares to help his team make a playoff run.
The Texans, under former GM Rick Smith, did not usually negotiate contracts during the regular season. However, when asked about his deal getting done ahead of the playoffs, Mercilus told reporters he wasn't surprised the two sides reached an agreement.
"Changing up some things versus what they've done in the past and just being better as far as keeping whatever talent they want around before free agency, or whatever the case may be, but it didn't really shock me."
Mercilus said even if a deal during the season wasn't in the cards, it wouldn't have bothered him at all.
"Either way, flip of the coin, it didn't really matter to me. Whether I hit free agency or whatnot, that would have been the first of my career, but I'm happy to be a Texan for the long-term now."