DeMatha cruised by Gonzaga, 79-66, and St. John's got past McNamara on a late rally, 63-56. (Video by Josh Apple for Synthesis/Koubaroulis LLC./The Washington Post)

As a sophomore slotted behind a St. John’s starting back court of Division I recruits, Tre Wood enters most games with little idea of how much he’ll play — and he’s fine with that.

But on Sunday, with a spot in the WCAC boys’ basketball championship on the line and the Cadets’ starters struggling to fend off McNamara, Wood momentarily shed his patient approach.

After knifing into the lane for one of his three buckets on the evening, Wood energized the Cadets on both ends of the floor with airtight defense and playmaking passes during a fourth-quarter run that sealed a 63-56 win for No. 2 St. John’s over the Mustangs at American University’s Bender Arena.

The Cadets advance to Monday’s championship, where they will face No. 3 DeMatha, a 79-66 winner against No. 9 Gonzaga in Sunday’s other semifinal.

“I understand it’s a process with earning time on the floor, so for now, it’s about making the most of what time I do get,” said Wood, who finished with eight points. “I saw ways to help my team and help pick up our play, and the rest took care of itself.”

The Cadets (27-3) cruised through the game’s opening minutes, knocking down jumpers and attacking the rim in transition to build a 15-0 lead.

Standing on the verge of a blowout, McNamara (17-12) ultimately caught up with St. John’s by slowing the game’s pace. Six-foot-nine freshman Makhi Mitchell went to work against the Cadets’ smaller forwards, scoring 15 points, including a three-point play that cut the halftime deficit to 28-20. Jamir Moultrie then accelerated the comeback in the third quarter with three three-pointers during an 11-2 run that gave the Mustangs their first lead.

“We started not getting the same stops that we had been getting before,” said Dejuan Clayton, who had 12 points. “We huddled up and kept calm and said we need to play unselfish to get back in the game.”

Clayton responded with a corner three-pointer that halted the Mustangs’ run. Then, following Wood’s bucket and a big block, Anthony Cowan Jr. , who had struggled to find his stroke, nailed a three off a crossover during a 15-0 run that iced the win.

Stags roll past Gonzaga

As DeMatha senior Nate Darling leaned up off the floor after converting a twisting layup while being fouled early in Sunday’s game with Gonzaga, he clenched his fists and let out a yell that resonated throughout the packed arena.

With the game still in its opening moments, the play itself might not have been conclusive, but Darling’s reaction was, an indicator of the Stags’ determination to settle the score with their WCAC rivals.

Playing off that attitude, Markelle Fultz scored 10 of the team’s next 12 points, including a thunderous dunk, to spark DeMatha in its 79-66 win over the Eagles.

“Last year hurt losing to them in the championship, so I had a little extra kick in my game,” said Fultz, who finished with 21 points for the Stags (26-4). “Whatever we had to do to win this game, we were ready to do it.”

For Fultz, that meant leading the effort to contain electrifying Gonzaga guard Chris Lykes. Though the junior finished with a game-high 28 points for the Eagles (22-7), DeMatha’s defense limited Lykes from getting his other teammates involved with several zone looks.

The Stags, on the other hand, featured five players with at least eight points, led by Fultz, D.J. Harvey (15 points) and Darling (14 points), sending DeMatha back to the tournament final for a third straight season.