BERKELEY, Calif. -- After one of Washington's best starts ever and an impressive unbeaten five weeks, the Huskies suddenly have some serious concerns at the start of the Pac-12 season.

They're on a two-game losing streak.

Jordan Mathews scored 31 points and knocked down three of his career-high five 3-pointers in the second half, leading California to an 81-75 upset of No. 21 Washington on Friday night in the Pac-12 opener for both schools.

Washington shot 53.6 percent in the first half then 38.2 over the final 20 minutes. The Huskies hurt themselves with 12 turnovers and breakdowns on both ends that allowed Cal to establish a nice tempo and shoot 60.9 percent after halftime.

Nigel Williams-Goss had 19 points, eight rebounds and nine assists and Robert Upshaw added 16 points, eight boards and five blocks for Lorenzo Romar's Huskies, who lost their second straight and still must play a tough game at Stanford on Sunday in jeopardy of falling out of the Top-25 poll. Washington has dropped the last three against Cal (11-3, 1-0 Pac-12).

"Not to discredit them in any way, they played a great game and offensively they executed sets, but a lot of things in the second half were just defensive mishaps," Williams-Goss said. "Shooting 60 percent from the field, you have to credit them for making shots, but they're getting a lot of open looks if they shoot that high of a percentage. A lot of that is on us."

David Kravish had a career-high 21 points and 10 rebounds for the Golden Bears, who had lost consecutive games for the first time under new coach Cuonzo Martin.

Quevyn Winters missed an open 3 with 13 seconds left that would have made it a one-possession game. The Huskies (11-2, 0-1), ranked No. 13 in the previous poll, were stunned 62-57 at home by Stony Brook last Sunday.

Mathews shot 8-for-14, hitting a 3-pointer with 6:37 remaining moments after Mike Anderson's 3 on the other end had pulled the Huskies to 56-52. Mathews scored again from long ranger at 4:18 and also converted 10 of 12 free throws.

"Mathews hit some tough shots," Romar said. "They scored a third of their points off offensive putbacks and off of our turnovers. They capitalized when they needed to. We missed a lot of shots."

Jernard Jarreau converted a three-point play, then Williams-Goss made a steal and layin, then converted two free throws with 4:40 left to pull Washington within 61-59.

Mathews delivered again to keep Cal ahead, and he finished with four or more 3s in a game for the fourth time in his career.

"When we got guys going like that on offense, it kind of takes the edge off for everybody," Kravish said.

The Bears established their tempo on the fast break early in the second. The Huskies committed three turnovers in a span of 2:37 as Cal took a 43-38 lead at the 13:26 mark of the second half on Tyrone Wallace's layin.

Wallace wound up with 19 points and shot 11-for-12 from the line for Cal, which concluded the non-conference schedule with at least 10 wins for the first time since also beginning the 2011-12 season 10-3. The Bears were 24-of-34 overall on free throws.

"We have to be sound defensively and make free throws," Martin said. "When you make free throws, it opens it up."

The Bears, who came in holding opponents to 59.7 points per game, also swarmed the middle defensively in the second half to slow down the 7-footer Upshaw. He made only two shots over the final 20 minutes.

Cal missed 10 straight field-goal tries midway through the first half, a stretch of 5:08 between Kravish's two baskets.

MATHEWS FACTOR

Washington put its defensive energy into stopping Wallace, who was held to 4-for-20 and missed all four of his 3-point attempts. But Mathews kept hitting the key shots.

"Any time someone can get 30, I guess you'd call them the X factor," Williams-Goss said. "Tyrone was definitely our main priority coming into the game. He was averaging 19 points a game."

TIP-INS

Washington: Upshaw has 60 blocks and is seven from tying the UW single-season record held by David Dixon and Christian Welp. ... Williams-Goss has 89 assists through 13 games.

California: Cal hosted Washington in its conference home opener for the third straight year. The Bears are 9-4 in conference openers dating to 2003. They beat the Huskies during the five-game winning streak in Pac-12 play starting last season. ... Cal is 8-2 at home in Haas Pavilion.

UP NEXT

Washington: At Stanford on Sunday night.

Cal: Hosts Washington State on Sunday.