The American star sits atop the leaderboard on 11 under par after shooting a flawless 65 on Saturday -- his third consecutive round in the 60s -- while compatriot Matt Kuchar is his nearest challenge at eight-under.

Spieth, winner of the Masters and US Open in 2015, had held a two-stroke lead over Kuchar at the halfway stage and kept his rival at bay all afternoon on Saturday before extending the advantage when he birdied the 18th.

Spieth has been at the top of the leaderboard after each of the first three rounds this week, but as he comes into the finale memories are still fresh of his stunning collapse in the last round of the 2016 Masters.

Then he led after each of the first three rounds and was five shots clear approaching the 10th hole on the Sunday, only to drop six shots in three holes and eventually lose out to England's Danny Willett.

"I think I'm in a position where it can be very advantageous, just everything I've gone through, the good, the bad, and everything in the middle," said the world number three when asked if he would use that experience to his advantage on Sunday.

"I understand that leads can be squandered quickly, and I also understand how you can keep on rolling on one."

If the Texan sees out the victory he will follow in the footsteps of the great Jack Nicklaus by getting three-quarters of the way to a grand slam in the majors before his 24th birthday -- he turns 24 next week.

Kuchar, 39, has never triumphed in a major but then the last seven majors have all gone to first-time winners and five of the last six British Opens have been won by players aged 39 or older.

The duo will be the last pair out on the course as they tee off at 2:30pm local time (1330 GMT) on Sunday afternoon.

"I'll be playing with him but not focused on him. My goal is to go out and play Royal Birkdale," said the giant Florida-born Kuchar, whose best finish at a major to date is tied third at the Masters in 2012.

"I'll know exactly where we stand but I don't know how much that ever helps you. You just have to go out and hit the best shot for the situation."

- 'Be aggressive' -

Behind Kuchar, there is a gap to Canada's 20-year-old Open debutant Austin Connelly and current US Open champion Brooks Koepka, who are both on five under par. They tee off at 2:20pm.

"You've got to be aggressive if you want to win. Conservatively aggressive, I guess you could say is the best way to put that," said Koepka on Saturday.

"I can't make mistakes with bogeys tomorrow if I want to catch them."

Japan's world number two Hideki Matsuyama and Branden Grace of South Africa are both four-under with the latter fresh from becoming the first player ever to shoot a round of 62 in a major championship on Saturday.

Grace took advantage of benign conditions as he made history and the forecast is for largely fine weather throughout Sunday, although there could be rain later on.

Chan Kim, Sweden's defending champion Henrik Stenson and world number one Dustin Johnson are all three-under, surely too far back to threaten Spieth.

Five of the nine previous Opens held at Birkdale, on the Irish Sea coast in the town of Southport near Liverpool, have produced American winners, including Arnold Palmer in 1961 and Tom Watson in 1983.

Willett, whose career has not really kicked on since he beat Spieth to the green jacket at Augusta last year, was handed the first tee time on Sunday at 7:55am.

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