Bears guard MaCio Teague, the team's leading scorer in Big 12 play, sat out for the second straight game with a wrist injury.
The Sooners were hosting a No. 1 team for the first time in 23 years.
Oklahoma opened with a 10-5 lead, but Baylor's tough defense smothered the Sooners for most of the first half. The Bears took a 28-19 lead before Brady Manek connected on a 3-pointer and an alley-oop dunk to trim the deficit to four. Baylor led 30-24 at halftime.
Oklahoma trailed 39-38 and could have taken the lead, but Doolittle missed a 3-pointer that was a bit rushed. Baylor responded by scoring six straight to go up 45-38. A deep 3 by Butler put the Bears ahead 55-44 with about six minutes remaining.
Baylor hasn't trailed in the second half in nine straight games. The last time the Bears trailed after the break was Jan. 18 at Oklahoma State (trailed with 3:30 left).
With their win Tuesday, the Bears moved to 24-1 on the season, their one loss coming against Washington on Nov. 8 in Anchorage, Alaska.
Up next for Baylor is a visit from No. 3 Kansas Saturday at noon ET on ESPN. According to ESPN's Pregame Matchup Quality metric, the matchup is the best game in college basketball this season (99.0 rating out of 100).
The current AP top 5 is a combined 65-1 since Jan. 1, with the lone loss coming from Kansas against Baylor.
ESPN Stats & Information and The Associated Press contributed to this report.