Kreps provided victory just 13 seconds into overtime. He took a pass from Daniel Paille at the bottom of the left circle and snapped a shot in off the right goal post.
The Moose forced overtime with 42 seconds left in the third period when Jesse Schultz scored his second goal of the game.
Rochester improved to 13-1 while Manitoba fell to 5-8-2-2.
Schultz put the Moose ahead just 5:20 into the game. He took a pass from Brandon Reid in stride on the left wing, soared past defenceman Martin Lojek and tucked the puck past goalie Craig Anderson. But Lojek gained redemption at 10:18 by scoring his first goal of the season, driving a slap shot from the top of the right circle past goalie Dany Sabourin.
Kreps put the Americans ahead just 22 seconds later with his first goal. David Booth worked the puck free on the left-wing boards and Kreps then picked it up, moved into the left of the slot and, with Alex Edler in front of him, zipped a shot between the defenceman's legs and past Sabourin high on the short side.
Clarke MacArthur extended the lead to 3-1 with his eighth goal at 6:30 of the third period. He danced around Edler at the blue-line and darted down left of the slot before snapping a shot into the top right corner of the net.