St. Louis Catholic jumped out to an early 21-0 lead and fought the entire game to hold onto it.

But a huge defensive play clinched a 31-21 victory for the No. 9 Saints (6-5) over Thomas Jefferson (6-4) at Hoss Memtsas Stadium on Saturday afternoon in a Division II select first-round playoff game.

“Any win you get in a playoff game is huge,” St. Louis coach Charlie Cryer said. “We should’ve put it away in the first half, but we didn’t. I think we got a little uptight and a little lazy when we got the lead, but we pulled it through.”

The Jaguars forced a fumble by Saints running back Colby Rodriguez and had the ball with a chance to either tie the game or take the lead late in the fourth quarter.

Backed into a fourth-and-8, the Jaguars dropped quarterback Tyler Lavergne back to pass but St. Louis linebacker Zach Eisner crushed Lavergne with a blindside hit and forced the senior quarterback to fumble. Saints linebacker Mac Thompson scooped up the fumble and returned it 60 yards for a touchdown to extend their lead to 31-21.

“It was a great play by Zach Eisner, and I was just in the right place at the right time,” Thompson said. “We’ve been playing against the zone read all year, but we were preparing for their tight offense during this week. So when they started running the spread plays, it kind of caught us by surprise.

“But once we got settled in and started figuring out what they were doing, we started making plays.”

After a field goal extended the St. Louis lead to 24-14, Thomas Jefferson got runs of 47 and 7 yards from wide receiver Tyler Butler and running back Donte Sincere, respectively, before Butler suffered an apparent leg injury on a 12-yard run.

Lavergne took over his normal quarterbacking duties and finished off the seven-play, 93-yard drive with three runs of his own, including a 5-yard touchdown.

After both team’s exchanged interceptions on the next two drives, Jaguars linebacker David Lewis forced quarterback Cameron Fontenot into a fumble and linebacker Mohamed Monem scooped it up and returned it 17 yards for a touchdown to cut the St. Louis lead to 24-21.

“That was a huge play for us, but we never were quite able to get over the hump,” Thomas Jefferson coach Kevin Kelly said. “We make that play, then turn around and throw another interception in the red zone.”

With their offense only managing 69 total yards through the first 22 minutes of the game, the Jaguars turned to their trusted “T-But” package — which features Butler at quarterback — to put together their best drive of the half.

Butler ran the ball six times and gained 47 yards during an eight-play drive that covered 66 yards and ended with him running in a 2-yard touchdown with seven seconds left in the half to cut the St. Louis lead to 21-7 heading into halftime.

“He’s been playing with an MCL tear and just wearing a brace on it, so we just wanted to be careful,” Kelly said of Butler. “He tweaked it earlier in the game and then he tweaked it again later, and we didn’t want to do anything to ruin his knee so we took him out the game.

“But it shows you how tough he is to play through it for as long as he has.”

Butler finished with 11 carries for 115 yards and a touchdown before exiting in the third quarter.

After stuffing Sincere on a fourth-down play in its own territory, St. Louis made the Jaguars pay when Rodriguez took a handoff 61 yards on the next play to extend the St. Louis lead to 21-0.

“We just executed,” Cryer said. “Our defense made some big plays early, and we were able to turn around and put points on the board immediately after forcing those mistakes, and that was huge for us. Our offense slowed down a little bit in the second half, but we did a great job of jumping on them early and making them adjust to us.”

After a Jaguars punt ended up netting negative yardage, the Saints only needed five plays to cover 31 yards, capped by a 17-yard touchdown throw from Fontenot to wide receiver Dekeinen Francois.

On the first play of the ensuing drive, Lavergne tried to hit a deep post to receiver Marlon Wilkins, but Saints cornerback Michael Mack snatched the pass away from Wilkins and returned it 36 yards into the Jaguars territory.

The next play, Fontenot connected with Francois again for a one-handed, 22-yard touchdown pass up the seam to give the Saints a 14-0 lead with five minutes left in the first quarter.

Fontenot completed six of his 15 passes for 93 yards with two touchdowns and two interceptions. Francois had four catches for 74 yards and two touchdowns.

St. Louis will face No. 1 University Lab next week in the second round of the playoffs.