Doneeka Hodges, who led LSU with 23 points, scored the Tigers' first seven points of the second half during a 12-2 run that produced a 39-39 tie.
Bjorklund, playing 31 minutes in place of injured starting center Britt Hartshorn, hit a free throw to put Colorado ahead for good at 42-41. Bjorklund then scored eight straight Colorado points as the Buffaloes built a 58-48 lead with 6:40 remaining, and Nightingale hit her 3-pointer a minute later.
LSU (18-12), the No. 6 seed, got no closer than seven points after that. Colorado hit 13 straight free throws in the final 10 minutes.
Two 3-pointers by Nightingale and one by Jenny Roulier put the Buffaloes ahead 11-4 with 12:57 left in the first half.
The Tigers, dressing only seven players, countered with a 13-2 run that started and ended on 3-pointers by Hodges, to take a 17-13 lead. The spurt included a three-point play by Aiysha Smith, who beat a double team on a layup. Colorado outscored LSU 24-10 the remainder of the half. The taller Buffaloes, who had failed to establish an inside presence against the quicker Tigers, got their first inside basket on a layup by Bjorklund with 10:00 remaining.
The Buffaloes scored 11 straight points, including Nightingale's driving layup and her two 15-foot jumpers, for a 34-25 lead. After LSU's Temeka Johnson hit a baseline jumper, Nightingale followed with a 3-pointer with four seconds left.