SAN FRANCISCO (AP) - Johnathan Williams scored 17 points and Josh Perkins added 16 to lead No. 15 Gonzaga to its 18th straight road victory in the West Coast Conference, 75-65 over San Francisco on Saturday night.

The Bulldogs (16-3, 6-0) got a rare test in conference play after winning their first five games by at least 29 points. But they were up to the task with help from two key blocked shots late by Rei Hachimura.

Silas Melson had 14 points and Hachimura added 10 as Gonzaga was held nearly 16 points below the its season average but still managed to win its 12th straight in the series.

Souley Boum scored 22 points and Frankie Ferrari added 18 for the Dons (10-9, 2-4). San Francisco has lost 14 straight games against ranked opponents since beating Gonzaga at home 66-65 on Feb. 12, 2012.

The Dons managed to cut what had been a 12-point deficit in the first half down to five on a 3-pointer by Ferrari early in the second half. But USF them missed seven of its next eight shots from the field as Gonzaga back up to 14 on a 3-pointer by Perkins just past the midpoint of the half.

USF didn't go away and cut it back to six on a 3-pointer by Jordan Ratinho and had a chance to get even closer but Hachimura blocked a drive by Ferrari.

Williams hit a jump hook on the other end to make it 71-63 with less than two minutes left and Hachimura added another block on Boum to help seal the win.

BIG PICTURE

Gonzaga: The Bulldogs had won their first five conference games by an average of 35.4 points per contest. They were tested a bit against USF but never really threatened. Playing a game that was at least relatively close in the second half should be a good tuneup for Gonzaga's next game, at home on Thursday against Saint Mary's, which is also unbeaten in conference play.

San Francisco: The Dons were short-handed without second-leading scorer Chase Foster (ankle) and Taavi Jurkatamm (concussion). That left them little margin for error against the more talented Bulldogs. USF squandered too many chances, missing six straight free throws, including a front end of a one-and-one during stretch of the first half.

UP NEXT

Gonzaga: Hosts Saint Mary's on Thursday night.

San Francisco: Hosts Santa Clara on Thursday night.