The seventh-seeded Gauchos (27-4) never trailed in building a 12-point lead in the first half. Then 10th-seeded Xavier rebounded to pull within one early in the second half, at 33-32, on a layup by Amy Waugh.
The teams later each had 6-0 runs, giving the Gauchos a 53-43 edge with 8:43 remaining.
The Musketeers (20-10) trimmed the margin to six points, at 68-62, with 31.9 seconds remaining on a free throw by Waugh, but a free throw by Kristen Mann and two by Debby Caine helped put away the victory for the Gauchos, who play Texas Tech on Tuesday.
Lindsay Taylor scored 13 points, and Mann and Jess Hansen added 12 each for Santa Barbara, which led, 33-27, at halftime.
Waugh scored 19 points, and Tara Boothe had 16 points and 12 rebounds for the Musketeers.