Saint Mary's (22-5, 9-3 West Coast Conference) pulled within one-half game of the conference lead behind No. 13 Gonzaga, which lost 74-66 at Loyola Marymount.
Samhan, the WCC's leading scorer at 21.5 points per game, scored 11 points and had 11 rebounds, his 17th double-double of the season. Samhan, who is also the league's top rebounder, made just 4 of 15 shots.
Brandon Johnson scored 15 points to lead San Diego (9-19, 2-10), which lost its fifth straight and has dropped 10 of 11. The Toreros shot 37.7 percent and were outrebounded 39-25.