Drew Timme scored 20 points and No. 2 Gonzaga made 14 of its first 15 shots from the field to send Saint Mary's to its worst home loss in 19 years with a 90-60 victory.
The Bulldogs turned the highly anticipated showdown between the fierce rivals into a laugher by taking a 20-point lead midway through the first half and never really letting up after that.
The loss was the most lopsided at home in coach Randy Bennett's 19 seasons, topping a 28-point defeat to Gonzaga in 2014.
Jordan Ford scored 23 points to lead Saint Mary's.