Bortles threw for 239 yards with two interceptions for the Jaguars (5-11).
He forced a fumble with his third sack in the fourth quarter and it was recovered by Mercilus.
Watt, playing without a cast for the first time since breaking his left hand Dec. 9, had three sacks, forced a fumble and recovered another one to help the Texans (9-7) to their third playoff berth and first since 2012.
The win completes a remarkable turnaround for the Texans, who have used four quarterbacks this season, and bounced back after starting the season 2-5.
Watt joins Reggie White as the only players in NFL history to have three 15-sack years in their first five years in the NFL.
Akeem Hunt ran for 25 yards later in that drive and Grimes capped it with a 3-yard touchdown run to make it 17-3 with about six minutes left in the second quarter,nfl jerseys china
"It's tough to end the year on a note like that," Bortles said. "I guess the good thing is that we have a lot of time to look at it and figure out how to fix it."
Andre Hal grabbed his team-leading fourth interception of the season and the Texans led 20-3 at halftime after a 51-yard field goal by Nick Novak on the ensuing drive.
"If you are behind in the game, they can pin their ears back," Bradley said. "That is one of the most talented rushers in the game for many years. He can be disruptive."
Brian Cushing forced a fumble by Denard Robinson that Watt recovered to give Houston the ball at the Jacksonville 42. Hoyer fumbled on the next play, but Houston left guard Xavier Su'a-Filo grabbed it in the air and turned it into an 8-yard gain.
Watt, who had been slowed by his injured hand in recent weeks, got to work early, sacking Bortles on the third play of the game for an 8-yard loss. He got up after the sack, held his wrist and wiggled the fingers on his left hand to display that he wasn't wearing a cast on his left hand.
Houston took a 3-0 lead with a 29-yard field goal with about 5? minutes remaining in the first quarter.
Brian Hoyer threw for 249 yards with a touchdown and an interception in his return after missing the past two games after his second concussion in less than a month,Discount NFL Jerseys
"Give a lot of credit to Houston and their front," Jacksonville coach Gus Bradley said. "They caused issues. We said some of these guys have the ability to disrupt the game, and they did ... here is a team that won our division and kind of as a measuring stick of where we are at and what we need to do."
Kareem Jackson added a score on an interception return in the fourth quarter to pad the lead,Cheap Nike NFL Jerseys
The Jaguars cut the lead to 10-3 on a 43-yard field goal later in the second.
Mercilus has a career-high 12 sacks this season and gives Houston two players with 10 or more sacks for the first time in franchise history.
And it led to another lopsided loss for the Jaguars.
Watt, who leads the NFL with 17 1/2 sacks, had a little fun after a sack in the third quarter when he did basically every dance that's been hot in the past year. He did the "whip", "nae nae",Wholesale Adidas Hockey Jerseys
, "dab" and finished by running off on the "da plug" twice.
Jonathan Grimes had a 12-yard touchdown reception and added a 3-yard rushing score in the second quarter to help Houston take a 20-3 lead by halftime.
Mercilus tied a career high with 3 1/2 sacks and forced a fumble and recovered one.
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. Watt and Whitney Mercilus combined for 6 1/2 sacks on a day when Houston set a franchise record with eight in a 30-6 victory that gave the Texans their first AFC South title since 2012.
HOUSTON (AP) — Jacksonville couldn't protect Blake Bortles on Sunday against the Houston Texans.
Houston left tackle Duane Brown had to be carted off the field near the end of the first quarter after injuring his right knee. Chris Clark took over and they continued the drive, pushing the lead to 10-0 when Grimes grabbed his first career touchdown reception on a 12-yard pass early in the second quarter.
"It's definitely disappointing. I have a sick feeling in my stomach," Jacksonville left tackle Luke Joeckel said. "I have to be better. That's all I am focusing on right now."