Rob Gronkowski spikes the ball after his first TD then takes out a pylon in the process. (AP)

FOXBORO — While the Patriots looked hungover defensively to start the game, the New England offense looked just as sluggish.

While the Bills were putting up 21 first-quarter points, the New England offense was in the dark.

Then, the flip got switched.

Rob Gronkowski found the end zone twice on passes from Tom Brady, including a 17-yarder on a corner route that put the Patriots ahead to stay with 1:32 left in the third quarter. The Patriots scored 49 unanswered points on their way to their 13th straight win.

It was the second straight game the Patriots dug out of an early hole. Against the Dolphins, it was 17-0 down at halftime.

“Man, well last game it was the second half and this one was the second quarter, so hopefully the switch starts in the first quarter in the next game,” Gronkowski said. “I mean, I don’t know what it was. We just turned the switch and hit it off and put up 49 points and the defense turned the switch, too. They put up 21 points on us in the first quarter and then they shut them out the rest of the game, so that was unbelievable. We were playing complementary football at the end of the game and the second quarter and throughout. We go to [keep] playing like that [in] the playoffs.”

Gronkowski finished the single greatest season ever by an NFL tight end with 90 catches, an NFL-record 17 receiving touchdowns and an NFL-record 1,327 yards.

He can thank Bill Belichick for the final one.

With backup Brian Hoyer in at quarterback and the Patriots leading, 49-21, Belichick called a play for Gronkowski with under a minute remaining. The 22-yard reception along the left sideline gave Gronkowski the new NFL receiving record for tight ends, as Gronkowski finished with 1,327 yards for the season, 17 more than Jimmy Graham of the Saints, who finished their game with the Panthers several minutes earlier.

“Maybe, hahaha,” Gronkowski joked when asked if he and the Patriots knew about the record. “Yeah, obviously, why else would we call a play at the end when we could knee it. It’s just kind of obvious. I’m not going to lie about it. Yes, we knew. It means a lot, that they’re willing to do that and we can take a knee and make sure no one gets hurt or anything. It’s just an honor to play here.

“That’s why I love to playing here, great teammates, great coaches and everyone is just [about] the team here. Nothing would get accomplished here without everyone, all the vets. All the praise to all of my teammates and coaches.”

Gronkowski, who caught two touchdowns on the day, finished the season with 17 TD receptions and one TD rush and gave credit to fellow tight end Aaron Hernandez, who finished with 138 yards on seven catches.

“Playing with Aaron next to me, he balled out today,” Gronkowski said. “It’s great having him. He didn’t play versus Buffalo last time, and that just showed how big of a difference he is coming back and playing against him.”

Still, even Gronkowski realizes you can’t ask Brady to do it every week.

“Oh I know, definitely, we don’t want to be doing that,” Gronkowski said of overcoming deficits. “It’s the playoffs now. We got the best teams coming in the house, so we got to start in the first quarter, we got to start fast, we got to start strong and we can’t be getting down like that. We were lucky enough to even come back against Buffalo losing by that much – 21. We got to start fast for sure and we got to play all four quarters.”