Al Horford had 18 points and eight rebounds, Isaiah Thomas scored 16 points, and the top-seeded Boston Celtics beat the Bulls 104-87 on Friday night after dropping the first two games of their opening-round series at home.The Celtics pulled away after a 20-point lead shrunk to one early in the third quarter and put themselves in position to tie a series that was in danger of slipping away from them. Game 4 is Sunday in the United Center.Dwyane Wade scored 18 and Jimmy Butler had 14 points on 7-of-21 shooting, and the offense simply didn’t click the way it had been, with Rajon Rondo out indefinitely with a broken right thumb. The Bulls shot about 39 percent and committed 18 turnovers.Thomas, grieving the death of his sister in a car accident last week, rejoined the team after spending time with his family in Tacoma, Washington. He scored eight points in the third quarter, helping the Celtics regain control.Jae Crowder finished with 16 points. Avery Bradley scored 15 and hit four of Boston’s 17 3-pointers.The Celtics’ lead was down to 44-43 early in the third when Thomas hit Horford for an alley-oop dunk and nailed back-to-back 3-pointers. Boston maintained a comfortable edge after that.The Celtics led by 18 after hitting 7 of 11 3-pointers in the first quarter and were up 37-17 early in the second before the Bulls jumped back into it.They had the crowd rocking in the closing minute of the half. Nikola Mirotic nailed a 3, cutting it to 44-41, and pointed toward the sky. Wade then blocked Bradley’s 3, causing a shot-clock violation with 4.7 seconds left, before Butler missed a desperation 3 for the Bulls as time expired.Celtics Coach Brad Stevens shook up the lineup looking for more shooting and athleticism. Gerald Green started over Amir Johnson and had eight points in 21 minutes.The Bulls are 121-50 all-time in home playoff games.Rondo, who was injured in Game 2, will probably be re-evaluated in a week to 10 days. The Bulls said he won’t need surgery.He watched from the sideline and got in on the action to some extent late in the first quarter. Crowder jawed at the Bulls’ bench after hitting a jumper and Rondo extended his leg as he walked by