Padraig Harrington scored a flawless 65 on a remarkable day of low scoring at St Andrews, while Irish amateur Paul Dunne finds himself vying for top spot on a congested leaderboard.

Harrington was unable to birdie the 18th but set the new clubhouse target on 10 under, currently two behind leader Dunne. Jordan Spieth, Danny Willett, Louis Oosthuizen and Jason Day sit one shot back on 11 under.

Dunne was in the second group out on Thursday morning and birdied the first two holes, joking afterwards he wondered if someone had taken a picture of the scoring computer as proof he had led the Open.

And after birdies on the 10th and 11th the 22-year-old amazingly held the outright lead once more, one shot ahead of Spieth, Harrington, Willett, Johnson and Australian Steven Bowditch.

The last amateur to win the Open was the legendary Bobby Jones in 1930, while Justin Rose was fourth at Birkdale in 1998 and Chris Wood fifth 10 years later at the same venue.

Jordan Spieth boosted his bid to become the first player for 62 years to win the year’s first three majors when he fired a six-under-par 66 in the British Open third round on Sunday.

The 21-year-old American, who began the day five under for the championship, sprinted through the field to take the early lead in the clubhouse on 11-under 205.

Spieth waved his putter like a magic wand to birdie the first, fifth, seventh, 10th, 11th, 12th and 15th holes, his only bogey of the day coming at the par-four ninth.

American Ben Hogan was the last player to capture the opening three majors of the season in 1953.