Guilmet scattered five hits over 7 2/3 innings before giving way to closer Daniel Schlereth who earned his third save of the young season.
Guilmet moved to 2-0 on the young season edging All-American pitcherWes Roemer. Roemer, who was the pitcher of record in 2005 when the Titans eliminated Arizona from the NCAA Tournament, also struck out nine but gave up the two runs of seven hits.
The Cats got on the board first thanks to some small ball. Kevin Rodland tripled promplty scored when the next batter, freshman Dwight Childs, sacrificed him with a long fly-out.
After Fullerton tied the game, the Cats came back in the fifth. Brad Glenn doubled down the left field line and Erik Castro's two-out single plated the game winner.
The Cats move to 9-0 on the season. The two teams meet again on Saturday at 7:00 pm MST.