Host B.J. Koubaroulis runs through the top plays from high school basketball games in D.C., Maryland and Virginia. (The Washington Post)

After becoming just the third school in Washington Catholic Athletic Conference history to go undefeated in regular-season conference play, Gonzaga knew its road to the WCAC tournament title would only get tougher.

That hard lesson surfaced Saturday, when an inability to make open looks coupled with an upstart Bishop Ireton team to make for a 67-58 upset loss in the quarterfinals.

“We missed 14 shots within five feet of the basket,” Gonzaga Coach Steve Turner said. “We were impatient at times, and they took advantage of that. When we were patient and able to get the ball in the paint, we missed a lot of easy looks.”

After Gonzaga jumped out to an early lead, Bishop Ireton stormed back in the second quarter behind the play of Patrick Moseh. The junior forward found open spots and got to the foul line often en route to a game-high 20 points, which helped the Cardinals hold off a late charge by the Eagles.

“Give credit to Ireton because they executed their gameplan well and made shots when it mattered most,” Turner said. “It seems like every time we had an opportunity to make a run, they would hit a dagger three or get in the lane.”

Gonzaga’s loss marks the first time since 2003 that the tournament’s top seed has been denied the crown. But despite the letdown, the Eagles’ season isn’t over.

As WCAC regular-season champs, Gonzaga earned a spot in the Alhambra Catholic Invitational, which will take place March 14-16 at Frostburg State University. So far, the field also includes defending champ DeMatha, Benedictine College Prep, host school Bishop Walsh, nationally ranked La Lumiere (Ind.) and St. Frances. . . .

The Alhambra tournament will also be a welcome extension to the season for DeMatha. For the fourth time this season, the Stags lost on a buzzer-beater as St. John’s guard Darian Bryant hit a half-court shot to give the Cadets’ a 57-55 win in the WCAC quarterfinals.

“We fought and scrapped, as did St. John’s, but in the end, they made one more play than we did,” Stags Coach Mike Jones said. “It’s a tough one, especially for our seniors.”

St. John’s Coach Sean McAloon had originally designed the final play for Tre Campbell, who was supposed to catch a pass from Bryant while streaking down the sideline. But after bobbling and nearly losing the ball, Bryant had no choice but to fire a shot from halfcourt.

“It felt good after I let it go and it went in,” Bryant said Sunday after the Cadets beat Bishop Ireton in the quarterfinals. “To be so close to losing and then get the win on a shot like that was exciting.”

The Cadets will face O’Connell in the WCAC final Tuesday at 8 p.m. at American’s Bender Arena. The Knights won both regular season meetings.