When the season opened in September, Sheldon Day was just a contingency. The veteran defensive tackle signed to the Washington Commanders’ practice squad, providing an experienced option should anything happen to starters Jonathan Allen or Daron Payne.

Now deep into the season with the playoffs in reach, Day, a fourth-round draft pick by the Jacksonville Jaguars in 2016, has emerged as a key piece of Washington’s defensive line, filling in while Allen recovered from surgery to repair a torn pectoral muscle to provide stability and consistency to the Commanders’ defensive front.

“He was a guy that when he did his workout, I was like, ‘Okay, he’s a little small,’” defensive coordinator Joe Whitt Jr. said of the 6-foot-1, 285-pound Day. “And I like big guys. I don’t like a bunch of little guys. But he plays thick and heavy, and he’s right where he needs to be. He’ll throw his hands. … He understands the blocking schemes and what’s coming at him, the lean and the balance of the offensive linemen if it’s run-pass. He gets all that. He’s been a very important part to our defense.”

Day’s performance in Sunday’s 36-33 comeback win against the Philadelphia Eagles made that much clear. In 33 defensive snaps, Day was integral to the Commanders’ second-half improvement against the run, producing a batted pass, three run stops and a quarterback hit.

The Commanders allowed 169 net rushing yards and an average of 6.2 yards per carry before contact to the Eagles in the first half. Saquon Barkley accounted for most of those yards, including a 68-yard touchdown, his second in the first quarter.

“A guy should never run that far without being touched,” Whitt said. “In the second half — actually, after that play — I said, ‘Okay, we’re just going to run pressure.’

Washington called more run blitzes at Philadelphia in the second half, holding it to 42 rushing yards and only 0.6 yards before contact per rush. Day’s reliability up front was a significant factor.

“He’s a lot like when I talk about consistency and being where you’re supposed to be,” Whitt added. “Like I talk about [defensive end Dorance Armstrong] — that’s what Sheldon is.”

Allen said he expects to play Sunday night against the Atlanta Falcons, but the team has not made an official announcement about his availability. Allen was placed on injured reserve in mid-October, with the belief at the time the injury would be season-ending.