HILTON HEAD ISLAND, S.C. — Jordan Spieth had a post-Masters letdown Thursday, shooting a 3-over 74 at the RBC Heritage to end his run of 16 straight rounds under par.

Spieth vowed his whirlwind, two-day celebration tour of New York after winning the green jacket Sunday wouldn’t affect his focus. But it was apparent early on at Harbour Town that Spieth was not at his Augusta National best.

Spieth was visibly frustrated on the eighth hole when his second shot from pine straw landed well short of the green.

The 21-year-old Texan was eight shots behind leaders Graeme McDowell and Matt Every, who were at 5-under 66. Spieth will need significant improvement Friday to make his eighth consecutive cut.

“Got a good feeling about tomorrow,” Spieth said. “Feel like I got some swings in, got in somewhat of a rhythm and can at least go out and feel the shots. It was just an off day and it happens.”

It can happen more often after a few days like Spieth had.

He got into Sea Pines Resort late Tuesday night after some 25 appearances and interviews in New York, including an appearance with David Letterman.