George Mason began a men’s basketball season of high expectations Tuesday with a performance that failed to meet the standards set by a team returning every player and aiming to contend in the Atlantic 10.

The Patriots enjoyed stretches of prosperity but faltered defensively in the second half and faded down the stretch, losing to Pennsylvania, 72-71, before 5,767 at EagleBank Arena.

They squandered a late five-point lead and fell behind on AJ Brodeur’s free throw with 20 seconds left. The Quakers then missed five consecutive free throws, but the Patriots missed from close range, failed to secure a defensive rebound and watched Otis Livingston II’s running 15-footer fall short at the buzzer.

“When adversity hit,” said junior guard Justin Kier, “we didn’t respond.”

This from a team that won 10 of 11 close games last season and was picked to finish fourth in the 14-school conference, by far its highest preseason slot since joining the A-10 five years ago.

The Quakers shot 71 percent in the second half (17 of 24) and 54 percent overall, compensating for 6-for-18 free throw accuracy and the loss of their best player, Ryan Betley, who suffered a serious knee injury less than five minutes into the game.

“We took shots in the first half that we never take in practice,” Patriots Coach Dave Paulsen said. "We made defensive blunders in the second half that we never make in practice.

“When adversity hits, you have to get tighter with your culture, not go off on your own. When we played the way we practice, we were pretty good. But we probably did that for 24 or 25 of the 40 minutes.”

Paulsen received 15 points from Virginia transfer Jarred Reuter, but the 6-foot-7, 260-pound junior forward played just 17 minutes because of foul trouble and fatigue. Kier had 12 points, eight rebounds and three steals, and Livingston added 12 points.

Three reserves combined for 25 points and nine rebounds, but the Patriots committed 17 turnovers (one fewer than the Quakers) and scored on just three of their final eight possessions. They created high-percentage shots but weren’t efficient in the lane and, at the other end, conceded several easy baskets.

“Defense was the biggest thing,” Livingston said. “I take a lot of that on me. Being a senior, I am supposed to set the tone. I didn’t do that. ... We were starting to get to them but we couldn’t sustain it.”

The Patriots trailed most of the first half but found their way in the last five minutes. Opening-night nerves had contributed to unforced errors and early foul trouble.

Penn’s Michael Wang, a 6-10 reserve freshman, made four of five three-pointers before intermission and posted 14 points. The Patriots also had trouble with another big man, Brodeur, who scored eight in the first half and 19 in all.

Wang and Brodeur filled the void left by Betley, who had slipped under the basket and required extended medical assistance before being helped to the locker room.

“It’s not good,” said Quakers Coach Steve Donahue, whose team returned four starters and was picked second in the Ivy League behind Harvard. “We lose a great player, a great kid.”

Donahue added that Betley “ruined his knee” and would probably miss the season.

With Betley sidelined and the hosts beginning to settle down, the Patriots took a 37-33 lead into intermission when Kier beat the buzzer with a fast-break layup. The lead grew to nine in the second half, but the Quakers began scoring with ease against a soft defense.

The Patriots were ahead by five with four minutes left, then were outscored 9-3. They were up 71-69 with 1:26 left before Antonio Woods tied it on a drive through the lane.

George Mason’s Javon Greene missed inside with 40 seconds left. Brodeur made the go-ahead free throw and missed the next one. Kier missed with 10 seconds left. Brodeur missed two free throws, but Max Rothschild slapped the rebound to a teammate. Woods clanked two free throws, and Livingston fell short at the buzzer.

“We had really set out to create a defensive DNA,” said Paulsen, who is in his fourth season in Fairfax. “We played that way the last eight, 10, 12 minutes of the first half and the beginning of the second half and just didn’t sustain it. So that’s disappointing.”