Low scoring was the order of the day as the early starters took advantage of an almost defenceless Old Course at St Andrews in the 144th Open.

Torrential rain on Friday and winds gusting up to 45 miles per hour on Saturday had resulted in a Monday finish for just the second time in championship history, but conditions were ideal for the delayed final round.

New Zealand's Ryan Fox was in the first group out at 7:45am and fired six birdies and one bogey in a 67, while Australia's Scott Arnold went one better in the group behind with a flawless 66.

South Africa's Branden Grace had moved into a share of 15th thanks to a front nine of 31 and another birdie on the 10th before dropping a shot on the 16th, with Ryder Cup hero Jamie Donaldson also six under after 10 holes before a bogey on the 12th.

The top 25 players were separated by five shots, with Irish amateur Paul Dunne sharing the lead on 12 under par with 2010 champion Louis Oosthuizen and Australia's Jason Day and Jordan Spieth just a shot behind.

Dunne, 22, is the first amateur since Bobby Jones to lead the Open after 54 holes, the American going on to lift the Claret Jug at St Andrews in 1927.

Three years later, Jones became the last amateur winner of the Open to date at Royal Liverpool and went on to complete the 'Impregnable Quadrilateral' of Amateur Championship, Open Championship, US Open and US Amateur titles.

Spieth, 21, is seeking the third leg of an unprecedented calendar grand slam after victories in the Masters in April and last month's US Open.

Two-time Open champion Padraig Harrington was two shots off the lead, with Sergio Garcia, Justin Rose, Adam Scott and Danny Willett among a nine-way tie for sixth on nine under.