Gradnigo, who had 21 points, cut the Clemson lead to 59-58 a minute earlier with a 3-pointer. His missed runner in the lane was followed with a tip-back as time expired.
"Very disappointing loss, especially the fact that we had chances to make big stops at the end of the game and we didn't get a stop when we needed one," said Clemson head coach Brad Brownell.
The loss dropped Clemson to 2-2 on the season.
Tanner Smith, the Tigers' second leading scorer with nine points, said he's trouble by the consecutive losses to opponents from mid-major conferences.
"It's not something this program's used to," he said. "It's not something I know that guys watching on TV who played on this gym that played for Clemson, [they] probably aren't very happy with our performance right now. That's something we need to take pride in."
Andre Young , who shot 6 of 12 from the field, led Clemson with 20 points.
"We've just got to re-group. We've got to stop making the same mistakes," he said.
Clemson held Coastal Carolina scoreless until Anthony Raffa, who finished with 21 points, hit a pair of free throws with 16:37 remaining in the first half. The Chanticleers went without a bucket from the field until Jordan Griffin knocked down a 3-pointer with 13:55 left in the opening period.
After Coastal Carolina took a 19-17 lead with 5:53 left in the first half, Andre Young led a 16-2 Clemson run. During that stretch, the senior guard scored 12 points as the Tigers led by as many as 11.
Clemson took a 33-25 into the locker room at halftime.
Less than five minutes into the second period, Coastal Carolina cut the lead to 38-37 after back-to-back turnovers by Clemson led to fast break layups by Raffa.
"We struggled offensively in the second half," Brownell said. "Guys got a little tight, made some silly passers, had turnovers that led to fast break layups. That's really how they got back into the game. We don't do that and make them score against our set defense, it's hard for them to make up 12 points"
The Chanticleers went up 41-40 when Gradnigo hit a 12-foot jumper from the baseline at the 12:13 mark -- their first lead of the second half. Young put the Tigers back up on the ensuing possession with a slashing layup.
Kierre Greenwood, Coastal Carolina's second leading scorer was held without a basket for the first 31 minutes. The Chanticleers' best shooter went 1-of-3 from the field.
Clemson responded with a 6-0 run after Greenwood's free throws gave Coastal Carolina a 45-42 lead.
Another Raffa steal and fast break layup tied the score at 50 with 4:40 to play. The Tigers regained the when Young knocked down a corner 3 on the ensuing possession.
"To their credit, they had a couple of guys step up and make plays," Brownell said.
Clemson is back in action Friday night when Furman visits Littlejohn Coliseum.
Coastal upsets Clemson
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