Jared Dudley scored 25 points for BC (12-4, 1-3), including a second-chance dunk that put the Eagles up 85-81 after Florida State (11-3, 2-2) hit two 3-pointers to cut a 14-point deficit to two.
Alexander Johnson hit a 3 with 2:07 left, and Todd Galloway made one with 1:17 left to make it 83-81. Louis Hinnant of the Eagles drove to the basket but missed, but Sean Williams got the rebound and tucked a pass underneath to Dudley, who slammed it through.
Thornton made a couple of running bank shots, but Hinnant made four straight foul shots in the final 28 seconds and intercepted a desperation inbounds pass with 0.5 seconds left to clinch it.
Hinnant had 12 points and six assists for BC, which trailed by 11 points in the first half before opening an 80-66 lead with 5:36 to play. The win snapped a two-game losing streak and a three-game slide in the ACC for the Eagles as they start their first season since defecting from the Big East.
Thornton had 17 points in the first half and made three baskets in the final 29 seconds for the Seminoles, who had never played BC before. In all, he was 15-of-18 from the field and 6-of-8 from the line to surpass the career scoring high he set in a victory over Alcorn State on Nov. 21.
Florida State has a week off before playing No. 20 North Carolina, which lost 81-70 to Miami on Saturday. The Seminoles were trying to match their win total from last season (12-19) and win three straight in the ACC for the first time in 11 years.
Florida State led 33-22 in the first half before BC scored eight consecutive points, four on putbacks, to cut the deficit to three. The Eagles trailed 38-34 at halftime.
The Eagles were 1-for-7 from 3-point range in the first half and 8-for-12 in the second, making five in a row early in the second half to turn a two-point deficit into a six-point lead.
Smith was 12-for-14 from the line.
Florida State drops to 2-2 in ACC play
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