Washington missed its chance to take an unbeaten record into conference play when it couldn't overcome a poor shooting performance.
In their Pac-12 opener Friday night, the No. 21 Huskies will face a California team that also had a disappointing finish to its nonconference season.
Washington (11-1) was looking for its best start since 1975-76 when it faced visiting Stony Brook on Sunday, but shot a season-low 34.3 percent and lost 62-57. The Huskies blew a 16-point lead in the second half and scored four points in the final eight minutes.
Leading scorer Nigel Williams-Goss had 10 points - he averages 13.4 - and shot 5 of 14. Only two Washington two players reached double figures, with Robert Upshaw totaling 10 points, 11 rebounds, four blocks and two steals.
"Mentally, we just weren't there," coach Lorenzo Romar said. "And with so much at stake, you wonder why not. Obviously, me as the head coach, should have had our guys better prepared to go out and finish this up, but I didn't do a good enough job, obviously."
Cal enters Pac-12 play having lost back-to-back games after winning 10 of its first 11 under first-year coach Cuonzo Martin, their best start since 1959-60.
Cal has struggled at times with its shooting and its 39.1 percent performance in Sunday's 55-52 loss marked the fifth time it's been held under 40.0. The Bears shot 38.9 percent against the Badgers.
"It's just getting reps up and getting in the gym," said Martin, whose team also committed 18 turnovers. "The only way you get confidence is putting the reps in and then you start to see the shots fall."
Cal beat Washington by a combined 39 in the two meetings last season - taking an 80-78 series lead - and allowed a combined 33.1 percent shooting mark. The Bears avoided a third consecutive home loss to the Huskies with an 82-56 rout Jan. 15, holding them to a season-low 30.2 percent from the field.
Cal boasts the Pac-12's second-leading scorer, Tyrone Wallace, who averages 19.2 points. He scored a combined 34 and shot 12 of 24 in the two matchups last season.
The Bears are missing one of their other top scorers, Jabari Bird, due to a foot injury that's expected to keep him out for at least two more weeks. The sophomore guard is averaging 11.7 points and 2.5 assists.
Upshaw is the leading shot blocker in the nation at 4.6 per game and needs 12 more to tie the school's single-season record.
Washington is facing Cal as a ranked team for the first time since a 92-71 road win Jan. 16, 2011. The Huskies have split their last four matchups with the Bears when they've been in the AP Top 25.