FOXBORO, Mass. -- Stephon Gilmore's season-ending injury gave J.C. Jackson an opportunity to prove he truly is one of the NFL's top cornerbacks.
Instead, Jackson showed he still has a ways to go.
Elevated to CB1 status with Gilmore sidelined until 2021, Jackson drew primary coverage responsibilities on star receiver Stefon Diggs in the New England Patriots' Monday night matchup with the Buffalo Bills.
Diggs, like his team, won in a rout, finishing with nine catches on 11 targets for 145 yards and three touchdowns as the Bills coasted to a 38-9 victory at Gillette Stadium.
Jackson was in coverage on two of those scores: a 50-yarder late in the second quarter and an 18-yarder on the opening drive of the third.
“Honestly, I feel like I could have played better," he said in a postgame video conference. "I've just got to keep working, keep trying to get better. That's really it."
It was a humbling result for Jackson, a borderline Pro Bowler this season whose exclusion from the AFC squad was met with criticism last week.
Jackson ranks second in the NFL with eight interceptions and was fourth in passer rating against entering Monday, but he's greatly benefited from Gilmore's presence. With the 2019 NFL Defensive Player of the Year typically tracking each opponent's No. 1 receiver, Jackson sees more favorable matchups than most top corners.
Without that safety net, Jackson has not been the same dominant cover man. His three worst statistical performances of the season -- including a Week 8 loss to the Bills in which Diggs caught six passes for 92 yards -- have come in games Gilmore missed due to injury.
Monday's outing began promisingly enough for Jackson. Diggs' first three official targets resulted in two incompletions and a 2-yard gain on first-and-10. Jackson also had an interception in the end zone during this span that was wiped away by an offsides penalty.
ESPN cameras showed Jackson talking smack to Diggs after one of these head-to-head victories, which the Pro Bowl wideout did not appreciate.
"He was saying, 'Don’t play with me' and doing the No Fly Zone thing," Diggs told reporters after the game. "I don’t really like that very much. I don’t take too kindly to that. So I was just like, 'Relax.' "
Jackson's bravado aged poorly. Diggs, the NFL leader in both catches and receiving yards, beat him for touchdowns on Buffalo's next two possessions.
"I learned from it that each play, you can't take any reps off," Jackson said. "You can't fall asleep. You've got to be alert and ready every play when you're playing a receiver like that. He's a playmaker. He comes back to the ball better than any receiver in the league. He's got great hands.
"You've got to almost be perfect when you're guarding somebody like that. You've got to almost have perfect coverage in man-to-man."
Diggs' final three catches -- and his last touchdown, an 8-yard laser from quarterback Josh Allen early in the fourth quarter -- came with Jackson on the sideline. The Patriots replaced Jackson with second-year pro Joejuan Williams for one series in the second half, then sent him back onto the field for Buffalo's final two possessions. (Cornerback Jason McCourty was in coverage on Diggs' final touchdown.)
Asked what coaches told him during his temporary removal, Jackson replied: "I can't discuss that with the media."
Jackson, who's largely been excellent since joining the Patriots as an undrafted free agent in 2018, will be a restricted free agent this offseason. Gilmore's future with the team is unclear given his current contract situation.
