George Mason’s epic collapse Thursday night unfolded in steady, ruinous segments before culminating with decisive breakdowns.

A 20-point first-half lead crumbled, and when Drexel sophomore Damion Lee was done toying with them, the Patriots had dropped a 58-54 decision.

Lee scored 20 of his 29 points in the second half and made a go-ahead three-pointer with 22 seconds left as the Dragons won at Patriot Center for just the second time in 10 visits.

“This can be a house of horrors for us — we lost some huge games [by large margins] in here, some serious butt-whoopings up in this joint,” Drexel Coach Bruiser Flint said.

On this night, George Mason was the embarrassed one — and the timing couldn’t have been worse. At the start of three games in five days, the Patriots (12-9, 5-4) slipped into sixth in the Colonial Athletic Association and have to visit James Madison (13-10, 7-3) on Saturday.

After seizing a 33-13 lead, the Patriots were outscored 37-16 over 16 minutes. They were ahead by two with 21 / 2 minutes left on Sherrod Wright’s spinning layup but didn’t score again.

Lee tied it with a floater, and after a series of misses by both teams, he rolled off a screen and swished a three-pointer from the left wing for a 57-54 lead.

The Patriots did everything wrong down the stretch: Vertrail Vaughns stepped on the sideline with 14 seconds remaining. Drexel’s Frantz Massenat missed the front end of a one-and-one, but junior forward Jonathan Arledge fumbled the rebound out of bounds.

The Patriots fouled Lee, who also missed a free throw. But as Bryon Allen pushed the ball upcourt, Lee stole it from behind. Lee’s free throw with 2.2 seconds left sealed it for the Dragons (9-12, 5-4).

Patriots Coach Paul Hewitt cited poor rebounding for the collapse — a constant concern this season.

“We can’t allow people to be more physical and want the ball more than us,” he said. “I just felt like every key possession down the stretch, they were getting three shots.”

The Patriots were outrebounded, 26-12, in the second half and 39-28 overall. Lee, a 6-foot-6 guard, had nine rebounds — three more than George Mason’s leader, Erik Copes.

“Everyone has got to want to rebound,” said Arledge, who started in place of Johnny Williams (concussion) and had 14 points and five rebounds. “Everyone has got to want to get it.”

There were other problems. After shooting 54 percent in the first half and making four of their first six three-pointers, the Patriots were 28 percent from the field and 2 of 5 from the free throw line.

Wright, George Mason’s leading scorer, shot 1 of 6 after intermission and finished with 15.

It started so well. The Patriots didn’t allow a field goal in the first seven minutes and raced to a 12-1 lead. Later, Corey Edwards’s three-pointer upped the lead to 20, but the Dragons pulled within 38-25 at intermission on Lee’s buzzer-beating three-pointer – a harbinger for the second half.

“When we got it to 13, I said if we can get off to a good start in the second half, we’ve got a chance,” Flint said.

The Dragons scored seven straight after the break and eventually went ahead on Lee’s transition basket with 7:17 left.

Lee, who had 30 points against Delaware on Monday, dismantled the Patriots last season as well, scoring 16 in a five-minute stretch of the second half in Philadelphia.

“You can’t give him open looks,” Wright said. “Any type of open look, he is going to make.”