St. John’s poses after winning the WCAC baseball championship. (Daniel Gallen/For The Washington Post)

Sometime after A.J. Lee and Brett Simon doused St. John’s Coach Mark Gibbs with the water cooler but before Simon took a selfie of all of his teammates with their trophy, the team’s celebration of its second straight Washington Catholic Athletic Conference baseball championship took on a subdued but tense tone.

Somewhere, one of the Cadets had a shaving cream pie, and Gibbs knew who the intended target was.

“You better put that shaving cream down,” Gibbs said, eyeing his players warily as they gathered for yet another team photo on the turf at Shipley Field in College Park.

Moments later, Niko Jenkins reached around and pushed a metal pie tin into his coach’s face.

Sixth-ranked St. John’s had much to celebrate after its 12-1, five-inning victory over DeMatha in the decisive Game 3 of the WCAC finals.

The Cadets rallied after the Stags won the opening game of the series Friday night, staving off elimination Saturday afternoon to put themselves in position to clinch the program’s 16th championship Sunday. And in the process, they won back-to-back championships for the first time since the program captured three straight from 1976 to 1978.

“Since the season ended last year, we’ve just made it a mission to come out and make history,” said Lee, the Cadets’ Maryland-bound shortstop. “That was our little motto all year, to make history and win back-to-back championships. I know everyone on this team is ecstatic, and it’s just an amazing feeling.”

With the championship on the line, Gibbs handed the ball to the only freshman on the roster, right-hander Jake Steinberg.

The 15-year-old worked effectively and efficiently and faced the minimum through four innings. He set the tone by striking out DeMatha’s Aaron Brooks to open the game, and the Stags couldn’t solve his pitching.

When asked whether he was nervous to pitch in such a big game, Steinberg answered: “A little bit — I’m not going to lie — in the beginning. I just had to settle down.”

Steinberg’s lone hiccup came in the fifth when a pair of errors led to the lone DeMatha run. But with the bases loaded and one out, Steinberg forced a groundball to third baseman Myles Mensah, who stepped on third and fired the ball across the diamond for a game-ending double play.

Then the Cadets dogpiled in front of the mound.

“We don’t have very many freshmen that play that kind of role for us,” Gibbs said. “We’re very, very proud of him.”

While Steinberg dealt, the Cadets’ offense picked up right where it left off Saturday. St. John’s outscored DeMatha 24-3 in the final two games of the series after falling, 3-2, on Friday.

Soon, all that was left for the Cadets to do was pie their coach — again.

“We had those last year, and it seemed to work,” Lee said. “So we had to bring them back out.”