Jovanah Arrington scored 12 of her team-high 14 points after the break, and Mele Tupouata (11 points, 19 rebounds) pulled down 13 second-half boards to help Patterson extend its winning streak to 10 games.
After playing to an 18-18 tie at halftime, Patterson and Gregori stayed within two points of each other most of the second half in a back-and-forth matchup at Tracy High.
The third quarter featured four lead changes. Patterson's Kiara Job (10 rebounds), Janel Ortega and Shealyn Craven each scored four points in the period, which ended in a 32-32 stalemate.
The teams again traded leads early in the final period, before the Tigers were able to pull away for good.
Arrington connected on a pair of fourth-quarter 3-pointers, as she and Tupouata combined to score Patterson's final 17 points of the contest.
The Tigers (11-1) will face defending tournament champion Brookside Christian High of Stockton at 7:30 p.m. Saturday, Dec. 29 at Tracy High, for a chance to play for the tournament title.