Feeling no nerves since his Masters triumph, Jordan Spieth believes he can add a tartan jacket to his green one with victory in the Heritage on Sunday.

The 21-year-old world No.2 heads into the final round tied eighth and five shots behind winless leader Troy Merritt, who has a three-stroke advantage from defending champion Matt Kuchar, Brendon Todd and Kevin Kisner.

Spieth shot a three-under 68 third round while 29-year-old Merritt backed up his course record-equalling 61 with a 69 to get to 14-under 199 at Harbour Town Golf Links, claiming his first-ever 54-hole lead on the tour.

It was Spieth’s 18th time breaking par in his past 19 rounds, a month-long run of success that included the Valspar Championship title, seconds at Texas and Houston and that record-tying Masters win last week where he matched Tiger Woods’ mark of 18-under from 1997.

“Anything can happen around a course like this,” said a confident Spieth, welcoming his role as the hunter.

“There are eight-under and nine-under rounds out there. You have just got to get the right breaks.

“I am going to be aggressive tomorrow.

“The weird thing is this is the first time I have been in contention where I have not felt nervous.”

That’s in marked contrast to Merritt – but he welcomed the nerves.

“I was starting to feel the fear and being afraid, like I would when I was an amateur,” Merritt said.

“It’s not a bad fear; it’s the fear of being caught. And I think it’s worked for me in the past. “

Todd made the biggest move on Saturday with a 63 while Kisner shot 67 and Kuchar 68.

Jim Furyk led a group another stroke behind after a 68.

Rising star Cameron Smith had a round of 67 to be five-under for the tournament and the best-placed Australian in a tie for 27th.

Merritt’s best finish on the PGA Tour is a second in Memphis last year.

He moved to the top and built a four-shot lead on Friday with his course-record tying 61 at Harbour Town Golf Links.

He lost nearly all of that on the front nine on Saturday before regrouping.