Cleveland State found themselves in an unfamiliar situation on Thursday night at the Wolstein Center.
The Vikings had a 13 point lead against the reigning Horizon League tournament champs, but couldn't hold onto it.
Green Bay, who made just 23-of-41 shots from the free throw line, made 7-of-10 at the charity stripe in overtime and escaped with a 76-75 victory.
"This was a game we shouldn't have let get away," Vikings head coach Gary Waters said. "We had a lot of situations [to pull out the game], but we made too many errors down the stretch."
CSU (4-9, 0-1 Horizon League) had a chance to close out the game in regulation, but couldn't execute down the stretch.
With 37.4 seconds left, the Vikings held a two-point lead and had the ball coming out of a timeout, but they couldn't get the ball inbounds.
"All we had to do is throw the ball in and we win the game because they had to foul us," Waters said. "That was the worst play I've seen us make in a long time."
Green Bay stole the inbounce pass and Khalil Small's layup tied the game at 67-67.
The Phoenix (7-6, 1-0 Horizon League) also had a chance to win the game in regulation, but Tevin Findlay missed a pair of free throws in the final seconds.
The Vikings also missed on several opportunities in overtime.
On back-to-back possessions, CSU missed three point blank layups.
"Not so much a young team. It's a team that don't know how to win in the last minute yet," Waters said. "Is this a learning experience? - yes - but we got to gain from this or we lost everything we put in."
Kerem Kanter, the younger brother of the Oklahoma City Thunder's Enes Kanter, scored on a lay-up to give the Phoenix a 71-67 lead with 2:25 left in overtime. It was Green Bay's only field goal of the overtime session.
The Vikings fought back and tied the game at 75-75 on Rob Edwards' three-pointer with 16 seconds left.
"That was a big time three," Waters said.
With five seconds left, Trevor Anderson split a pair of free throws to give Green Bay the win.
The Vikings had one last chance to pull out the win, but couldn't get a shot off.
Edwards drove down the lane, but kicked the pass out to Tim Hasbargen, who couldn't get his three-pointer off in time.
"I should of pulled up," Edwards said on the final shot attempt. "I saw a guy ready to take a charge and had no other options."
Edwards led CSU with a game-high 22 points, 17 of them came in the second half and overtime. Bobby Word added 18 for the Vikings, who lost its first home game of the season.
Word was 4-of-5 from three-point range.
Charles Cooper led the Phoenix with 19 points, while Turner Botz added 12 and Kanter contributed 11 points and a career-high 14 rebounds.
"The one that really hurt us was Cooper," said Waters. "He came in and kept driving the ball. We never had an answer for him."
The Vikings turned it over 20 times and gave up 22 offensive rebounds.
"That was the game," Waters said about the differences in turnovers and offensive rebounds.
Word added: "I don't think we seen any pressure like that this year."
CSU will look to rebound Saturday when Milwaukee visits the Wolstein Center.