Justin Cobbs complemented Mathews' performance with a 20-point, 11-assist effort. Richard Solomon tacked on 16 points with nine rebounds for the Bears (11-4, 2-0 Pac-12).
Tyrone Wallace (14) and David Kravish (12) also reached double figures for the winners.
The Ducks (13-2, 1-2) have now lost two straight after starting the season 13-0. Oregon's first loss was to Colorado Sunday.
Oregon also had an 11-game home winning streak broken. The Ducks' last loss on their home floor came to California, 48-46 last Feb. 21.
Against the Bears, Joseph Young scored 29 points, including 16-of-17 from the free-throw line. Mike Moser recorded a double-double with 15 points and 10 rebounds.
The Ducks got 14 points from Johnathan Loyd and 10 from Damyean Dotson.