BOULDER, Colo. (AP) -- Oregon learned the hard way that protecting a lead is a lot harder than getting one.
Askia Booker scored a career-high 27 points, backcourtmate Spencer Dinwiddie had 23 and No. 20 Colorado rallied from a 10-point deficit in the second half to hand the 10th-ranked Ducks their first loss of the season, 100-91 on Sunday.
"I think we just got complacent with the lead and ended up giving them easy baskets," said Mike Moser, who led Oregon with 24 points. "We didn't defend at all how we wanted to. A lot of their best guys got going and we didn't do anything to slow them down."
Five-and-a-half minutes into the second half, Colorado found itself trailing by 10 points. From there, the Buffaloes got their transition game going, with Booker and Dinwiddie leading the charge down the court.
"We were attacking the basket, getting downhill, getting in the lane," Boyle said. "They play a matchup zone. They're so explosive offensively and they exert so much energy on the offensive end that sometimes defensively you can get them standing flatfooted and I thought Spence and 'Ski, our two guards, in the second half especially attacked the basket."
Xavier Johnson and Josh Scott had 15 points apiece for Colorado (13-2, 2-0 Pac-12), which is off to its best start since the 1968-69 team began the season 13-2. Scott had 12 rebounds for the Buffaloes, who remain unbeaten in 11 home games this season.
Joseph Young and Damyean Dotson added 16 points each for Oregon (13-1, 1-1), which was denied its first 14-0 start since 1937-38.
"We got the lead and we were so giddy about scoring baskets that we didn't guard," Oregon coach Dana Altman said. "We got the lead and held them to only five points in the first five minutes of the second half ... and then defensively, we broke down."
Leading the nation in scoring, Oregon, one of seven unbeaten Division I teams entering the day, could not keep up with Colorado.
Down 58-48 with 14:31 remaining, Colorado worked to get back within striking distance, and surged in front when Dinwiddie and Jaron Hopkins made 3-pointers around Johnson's layup for 64-62 lead.
Elgin Cook's layup with 6:32 left got the Ducks within 74-72 but they never regained the lead.
When Dotson's 3-pointer pulled Oregon to 80-75, Booker answered by converting a three-point play with 4:40 left.
Dotson's layup cut Colorado's lead to 91-86, but Booker made two free throws with 1:30 remaining to restore the Buffaloes' eight-point advantage.
Young connected on a 3-pointer for Oregon with 1:24 left but that proved to be Oregon's final field goal as Colorado made six of eight free throws down the stretch to seal the win.