SLU found itself in an early hole down 15-7 but stormed back with strong plays from freshman guard Jordair Jett. Towards the end of the first half, however, the Billikens once again found themselves in trouble down nine points. Another surge cut the deficit to just four points at halftime.
The Governors shot almost 54 percent in the opening half, while gaining a 16-11 edge on the boards.
SLU looked out of sorts on occasion, perhaps because they played four freshmen at times who are still learning the system.
"We've got inexperience issues," SLU coach Rick Majerus said. "You're dealing with four freshmen. They're playing in their first college game. They are playing along other freshmen. It's like a junior-college program."
Cassity said: "We had a lot of mistakes by everybody."
To start the second half, the Billikens came out firing and opened up a 45-40 lead after two straight buckets from Jett and a three-point play from Cassity. After a Cassity 3-pointer forced Austin Peay to call a timeout midway through the second half down 54-46, the Billikens could muster just eight points the rest of the way.
"We got stuck," Majerus said. "Dwayne (Evans) took that hook which was fancy, Christian (Salecich) missed all good shots."
Five straight empty trips down the floor spelled doom for SLU as the visiting Governors capitalized to tie the game at 54 apiece.
"We should have taken the momentum and ran with it," Cassity said. "But we didn't."
Tyshawn Edmondson buried two free throws with 4.2 seconds remaining to seal the game for Austin Peay.
"From now on, there's no looking back," Cassity said. "It will be good to get back out there. You don't want to sit back and recall this for too long."
The Billikens return to the court quickly as they will host Division II Rockhurst on Monday at Chaifetz Arena. SLU will then host Georgia on Saturday.