Georgetown’s Trey Mourning battles with Seton Hall’s Sandro Mamukelashvili for a rebound during the Pirates’ 73-57 win in the Big East quarterfinals Thursday night. (Brad Penner/USA Today Sports)

Georgetown’s seesaw of a season ended firmly in the mud Thursday night, and the landing could hardly have been messier at Madison Square Garden.

The sixth-seeded Hoyas lost, 73-57, to third-seed Seton Hall — a team they beat by six points in double overtime less than two weeks ago — in the quarterfinals of the Big East tournament to end Coach Patrick Ewing’s second season at the helm of his alma mater one win shy of 20 and all but squash the team’s NCAA tournament hopes.

Georgetown (19-13) likely needed a deep run in the Big East tournament to shore up a shaky NCAA tournament résumé, and Thursday’s loss was one the Hoyas could ill afford.

“I’m not sure what it’s going to be,” Ewing said when asked about his team’s chances of landing an at-large bid to the NCAA tournament. “It’s hard when you leave the decision in other people’s hands. We had an opportunity where, with wins, we would have had enough.”

Seton Hall (19-12) will play No. 2 seed Marquette in the semifinals. The Golden Eagles routed St. John’s, 86-54, earlier Thursday.

The most frustrating part for these Hoyas is that they have proven in the past month that they’re capable of winning big games. They did it with a 12-point win over Villanova, the six-point win over Seton Hall on March 2 and, most recently, a two-point win over No. 16 Marquette in the regular-season finale that earned the Hoyas a first-round bye in the Big East tournament.

What Georgetown has also shown is that it is a team incapable of capitalizing on momentum.

Those wins over Villanova and Seton Hall were both followed by bad losses. One more Thursday simply completed the pattern.

“I didn’t really say anything to the senior class,” Ewing said of his postgame speech. “I just said it’s disappointing, we have a good enough team that we could be playing tomorrow, but because we didn’t come with the right focus and the right effort, we fell short.”

Said James Akinjo: “Maturity. I think as a team, we’re not as mature as we need to be right now.”

Akinjo, the point guard, led the Hoyas with 15 points, and his fellow freshman Mac McClung had nine. Senior center Jessie Govan had eight points in his final Big East tournament game.

It was Seton Hall’s goal to attack Georgetown’s freshman core on defense.

“Our whole game plan was to make sure, if you can get young kids to stop and think what they’re doing on offense, it really takes them out of a rhythm,” Seton Hall Coach Kevin Willard said. “We were successful at home doing that. We were really successful actually there doing it, we just didn’t play well offensively there. Tonight was the same thing, just trying to get — Akinjo is so talented, McClung, and they play with so much emotion when they’re making shots. The biggest thing for us is to get them to try to stop and think, be aggressive with them, and just keep them off balance.”

That Seton Hall defense had forceful backup in Myles Powell, who scored a game-high 31 points. Myles Cale added 14 and Sandro Mamukelashvili added 12.

The Pirates had no trouble getting Georgetown out of sync early on, seized control midway through the first half and went into halftime with a 53-28 lead, leaving the once-rowdy, sellout crowd either headed toward the exits or slumped in their seats, hoping for some late drama that would never come.

Ewing said all week that starting the game with focus and effort was crucial against the Pirates. The Hoyas sprinted out to a quick 8-4 lead, making four of their first five field goals but looked jumpy along the way — their passes were often a hair overthrown, and the team rarely got the chance to get settled on defense as Seton Hall matched the breakneck pace.

Georgetown couldn’t sustain its energy level. And about three minutes in, the turnovers began.

The Pirates went on the first of many extended runs in the half just 2:30 into the game. Three Hoyas turnovers in 58 seconds led to a three-pointer from Cale, a dunk from Powell and a driving layup from Mamukelashvili that came in such a torrent that Georgetown’s players weren’t even back to defend.

Georgetown trailed 12-8 but wasn’t done giving the ball away; it had 10 turnovers and managed just nine field goals in those first 20 minutes. Seton Hall ended the game with 22 points off 14 Hoyas turnovers.

“I don’t think the moment is overwhelming,” Ewing said. “Even though it’s the Big East tournament, it’s a big game, but we’ve been in other big games . . . the turnovers, then the trap slowed us down. We weren’t able to get into a good flow, and that hurt.”

Powell not only outscored Georgetown with 29 first-half points, but he set a Big East tournament record for points in one half. To the Hoyas’ credit, they limited him to just two points after halftime. But the damage was done.

If this was Georgetown’s final game of the season — an NIT bid remains a possibility — the Hoyas did take a big step forward in Ewing’s second campaign.

Georgetown finished 9-9 in the Big East, which was four more wins than it managed last season, and made it to the quarterfinals of the league tournament for the first time since 2015. Akinjo was the first Big East freshman of the year from Georgetown in a decade. A loss at Syracuse was balanced out by a big road win at Illinois as well as wins over ranked teams in the Big East.

Ewing also turned his three freshman starters in Akinjo, McClung and Josh LeBlanc into leaders capable of dominating games, and he has plenty of frontcourt talent coming in next season — three recruits in addition to transfer Omer Yurtseven — to step in for the loss of Trey Mourning, Kaleb Johnson and Govan in the frontcourt.

“The difference is the freshmen,” Ewing said of the strides his team made. “The freshmen, they play great. They had their highs and their lows. For the most part, I thought that they had a great season.”