At Palouse Ridge Golf Club, Gabriel, who plays at St. Mary's, knocked off the No. 1 seed from Australia, 2 and 1, to advance to the Round of 32 on Wednesday.
Other first-round upsets included No. 49 Derek Bayley over No. 16 Li Wang, No. 48 Clay Christensen over No. 17 Cody McManus, No. 52 Clayton Madey over No. 13 Nicholaus Mandell, No. 44 Will Brink over No. 21 Matthew Rachey and No. 54 Alex Wagner over No. 11 Kevin Murphy.
Hans Reimers and Frank Garber, the Nos. 2 and 3 seeds, respectively, managed to advance.
Reimers, a recent Mercer graduate and former Oregon Open champion, defeated No. 63 Cale Lorenzi 2 and 1 to move on to Wednesday's scheduled Rounds of 32 and 16.
Garber, a rising junior from Washington, defeated No. 62 Dillon Jahns in 19 holes.
Following Wednesday's Round of 32 and 16 action, the quarterfinals and semifinals will be played Thursday before the 36-hole finale on Friday.
For a full look at the match-play tree, follow the results link below.