Swim great Michael Phelps upstaged some of golf's finest for one shot when he holed a 51-yard putt for a net hole-in-one during the second round of the Dunhill Links Championship on Friday.

Phelps, who is playing the team event off a handicap of 16, drove the front edge of the green at the par-4 sixth hole at Kingsbarns before sinking his lengthy downhill second-shot putt.

Because the winner of 18 Olympic gold medals had a stroke on the hole, he signed for a 'one' on his scorecard.

"That was the longest putt I've ever holed," he said.

"It was pretty incredible, watching it dive in was a pretty cool feeling. So to be able to have a net hole-in-one was pretty special.

"Even without that, this trip would have been very special, just having the opportunity to come over here and play amongst some of these players has been absolutely incredible."

Phelps proceeded to record a net eagle 'two' at the next for he and professional partner, Paul Casey, to eventually move to 9-under par overall.

Thailand's Thongchai Jaidee and his amateur partner, Hugh Courtney Jr., head the team format on 21 under.