Williams finished 19 of 33 for 263 yards, four touchdowns and an interception. The Toreros (9-1, 7-1 Pioneer Football League) won their eighth straight and earned the league's automatic bid to the FCS playoffs.
Ben Lehman's 3-yard touchdown pass to Spenser Pennington put Valparaiso (3-8, 1-6) up 27-26 with 28 seconds to play. Then San Diego returned the kickoff to its 34. Williams completed a 22-yard pass to Reggie Bell to set up the game-winning play.
Bell finished with five catches for 110 yards, White added five catches for 78 yards and two touchdowns, and Jonah Hodges ran 20 times for 169 yards.
Lehman was 20 of 30 for 221 yards, two touchdowns and an interception. He ran for another 41 yards and a score.