At Orono, Wilson Cheng headed in the game-winner inside the near post with 2:42 to play as the Red Riots tipped the Tigers of East Sullivan.
Cheng entered the game as a sub one minute before scoring the final goal for No. 7 Orono (7-6-2).
Tenth-seeded Sumner opened the scoring on a goal by Sam Barnes with 23:56 remaining in the first half. Tristan Rayner got the assist.
Orono scored the next two, by James Normand with an assist from Mathew Cloutier at 15:51 and by Cloutier with an assist from Justin White at 10:39.
Baramee Janla tied the game for Sumner (6-7-2) on a penalty kick with 27:42 left in the second half.