No. 1 Arizona 69, Colorado 57: Nick Johnson scored 18 points and the host Wildcats were never challenged in equaling a school record with their 19th consecutive victory.Brandon Ashley added 15 points as Arizona (19-0, 6-0 Pac-12) remained one of three unbeaten teams along with Syracuse and Wichita State. Freshman Aaron Gordon chipped in 12 points and Kaleb Tarczewski recorded seven points and eight rebounds for the Wildcats, who outscored the Buffaloes 44-26 in the paint.Xavier Johnson scored a season-high 21 points for Colorado (15-5, 4-3), which fell to 1-3 since star junior guard Spencer Dinwiddie went down with a season-ending knee injury. Josh Scott recorded 15 points and 11 rebounds while combining with Johnson to shoot 12-for-23 from the floor while their teammates shot 27.6 percent.Arizona scored the first nine points and led 18-4 as Colorado didn't make its first field goal until 5:23 had elapsed. A 10-2 run brought the Buffaloes within 20-14, but the Wildcats answered with a 12-2 spurt - capped by Johnson's breakaway dunk after Rondae Hollis-Jefferson's steal - en route to a 39-24 advantage at the break.Colorado's misfortunes reached a pinnacle when Scott inadvertently knocked Tarczewski's miss into the basket while trying to grab an uncontested rebound early in the second half. Arizona took a 51-31 lead on Gordon's reverse dunk with just over 15 minutes to play and didn't let the margin slip below 11 the rest of the way.GAME NOTEBOOK: Colorado has never beaten a No. 1 team in 16 tries. ... Arizona, which has won its conference games by an average of 17.2 points, previously won 19 straight during the 1992-93 and 1997-98 seasons. ... The Wildcats, who continued the best start in school history, recorded 16 assists, eight steals and seven turnovers.