The host Minutemen (13-1, 1-0) rallied from a 57-48 deficit, cutting St. Joe's lead to one on a drive to the basket by UMass' all-American candidate, Chaz Williams. Williams had a game-high 22 points.
Bembry received the inbounds pass but promptly had the ball stolen by Maxie Esho, who then dunked to put UMass up, 63-62.
"It's a turnover. There were 17 frustrating turnovers out there," Martelli said. "It's no more frustrating than opening the second half and missing three layups. Everybody that had a turnover is better than the turnover they had."
Trey Davis iced the victory for the home team by going 3 for 4 from the foul line in the last 33 seconds.
After Davis made it 65-62, Martelli called a timeout to set up a potential tying shot. The UMass defense was tough and Papa Ndao took a deep three-point shot as the shot clock ran down.
"Players just have to understand that there's more of the court to use," Martelli said. "It was almost like a youth soccer game broke out and everybody was like zeroed in on the ball."
In a game with nine lead changes and seven ties, the Hawks took a 31-28 lead into the locker room at halftime. They never led by more than nine points and couldn't put the game away.
The loss was costly for St. Joseph's as Ronald Roberts left the game with an injury early in the third quarter. Martelli said Roberts' back "seized up," and the forward's status for Saturday's game at George Mason was uncertain.