Shawn Moore made a layup to give UC Santa Barbara a 20-18 lead with 8:45 to play in the first half, and the Gauchos led 38-23 at the break. Sam Beeler made one of two free throws to stretch the Gauchos' lead to 20 points, 53-33 with 12:59 remaining.
Williams was 9 of 14 from the field. Kyle Boswell scored 15 points and Michael Bryson added 13 for UC Santa Barbara (21-8, 12-4 Big West) which ends the regular season one game back of conference-leader UC Irvine (22-10, 13-3).
Chris Eversley scored 14 points and was the only Mustang in double figures. Cal Poly (10-19, 6-10) has lost three straight and five of its last six games.