Kempker sank a bucket as time expired to lift Hart to a 55-53 win over Pentwater.
The Pirates led 15-10 after the first quarter and were up just 29-27 at halftime. Hart withstood Pentwater after it tied the score 41-41 in the third quarter.
Angel Salgado paced Hart with 15 points, Kempker finished with 12 points and 11 rebounds and Dustin Klotz had 11 points and 10 rebounds.
Glenn Miller drained six 3-pointers to pace the Falcons (12-6) with a game-high 25 points. Iain Stewart scored 10 points and Austin Hofmann chipped in eight points.