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 and seeing the view atop the Empire State Building.He acknowledged his preparation this week had suffered, but vowed not to have the major hangover several champions have when playing so soon after such success.
    Spieth was greeted by a large gallery on the first tee, crowds five and six deep stretching cellphones to snap pictures and get video footage. "Way to go, Jordan," someone shouted after his tee shot.
    The applause continued throughout the round and, while Spieth appreciated the sentiment, had difficulty concentrating on his game.
    "I was upset about missing the green and then there was a standing ovation walking up," he said. "It's like, 'Thank you. I just hit a terrible shot. Thanks.' So it was kind of tough to find the balance there."
    It was clear, though, this would not be the Spieth who tied the Masters' scoring mark of 18-under 270 set by Tiger Woods in 1997.
    He was in perfect position on the par-5 second, which played the easiest in round one, when he left his approach shot short and in the bunker. Spieth could not make an 8-footer to save birdie. He was short of the green again on the par-4 sixth hole, leading to the first of three bogeys — Spieth had just one bogey in his first 36 holes at Augusta National.
    "There's no excuses," he said.
    The wheels truly came off at the par-3 14th when Spieth hit into the water and watched his third shot spin back about 15 feet from the cup. He made a double-bogey 5.
    Spieth entered the week with four straight top-two finishes, also winning the Valspar Championship in a playoff at Innisbrock, finishing second in the Texas Open and losing in a playoff in the Houston Open.
    He hasn't had many days like this in 2015 — and neither had McDowell, who hadn't shot lower than 71 in his previous 12 rounds, including all four at last week's Masters when he tied for 52nd.
    McDowell, though, found his game on the layout's tight fairways and small greens. He had six birdies after an opening bogey to move in front.
    "It was great to feel comfortable out there today, see my lines, hit my speeds and make a few putts," said McDowell, who has not won on tour since taking this title in 2013.
    It's been a strange season for Every, who won the Arnold Palmer Invitational last month yet hadn't finished better than 27th in any of his 11 other events.
    He had birdies on four of his final eight holes, including a 50-foot chip in on the sixth hole and a 20-foot chip in on the seventh, to tie McDowell. Every stayed in the lead when he chipped to a foot on the eighth hole to save par.