LSU's Marcus Thornton shoots over Butler's Matt Howard (54) and Ronald Nored (5) during LSU's 75-71 win Thursday.
LSU’s Marcus Thornton shoots over Butler’s Matt Howard (54) and Ronald Nored (5) during LSU’s 75-71 win Thursday.

GREENSBORO, N.C. — Marcus Thornton wasn’t around for LSU’s last NCAA tournament appearance, stuck instead at a junior college while those other homegrown Tigers reached the Final Four.

He finally got his chance on the sport’s grandest stage, and played like he plans on hanging around for a while — especially when upset-minded Butler threatened to end things.

Thornton scored 30 points while coming through with one critical basket after another for hot-shooting LSU, which held off a late rally to beat the Bulldogs 75-71 on Thursday in the first round of the NCAA tournament.

Tasmin Mitchell had 14 points and Chris Johnson added 12 points and four blocked shots for the Tigers (27-7), seeded eighth in the South Regional. They built an early 13-point lead and shot 49 percent against one of the nation’s toughest defenses in advancing to Saturday’s second round to face top-seeded North Carolina, which routed Radford 101-58 in another first-round game.

“Did we think we were going to blow them out? We haven’t blown anybody out all year long,” coach Trent Johnson said. “We have a couple of guys that can make some plays, and when those guys don’t make plays, we have some other guys that are not afraid to step up and shoot the ball.”

Matt Howard scored 22 points before fouling out with 35.7 seconds left, and Shelvin Mack added 18 points for No. 9 seed Butler.

The Bulldogs (26-6) made things interesting by twice pulling within three in the final minute, the last coming when Willie Veasley tipped in Gordon Hayward’s missed 3 with 5.4 seconds left, making it 74-71. Johnson hit one of two free throws with 4.5 seconds left to seal it.

Hayward, Butler’s top 3-point shooter, finished with 12 points for the Bulldogs. The Horizon League regular-season champions were beaten in the first round for the first time since 2000.

Thornton, the Southeastern Conference’s player of the year, was 10-of-15 from the field and hit three of his four 3-pointers in his first 30-point game since last month against Georgia. Five of his baskets came when it was a one-possession game in the second half, including an impressive turnaround jumper with 141/2 minutes left that put the Tigers back up 43-42.