The 28-year-old Australian scored an eagle and six birdies during an eight-under 63 on the historic links of The Old Course, which means he has totalled 13-under 131.

This is the lowest 36-hole tally recorded in a major golf competition.

The stunning show by Smith, whose best performance in a major was finishing runner-up in the 2020 Masters Tournament, means he is two shots in front of first day leader Cameron Young of the United States.

The 25-year-old Young, equal third at this year's PGA Championship, blended five birdies with two bogeys to make three-under 69.

Northern Ireland's Rory McIlroy follows in third after cancelling two bogeys with six birdies.

The four-time major winner made 68 to tie Norway's Viktor Hovland on 10-under.

Hovland finished the second day with a six-under 66.

Dustin Johnson of the US posted a bogey-free 67 to be four off the pace while compatriot Scottie Scheffler, the world number one, is five off Smith.

Defending champion Collin Morikawa and golf great Tiger Woods, both from America, missed the cut.

Morikawa concluded his tournament on one-over par as Woods made three-over par.

The Scottish crowd gave Woods a standing ovation after completing the 18th hole in recognition that this could be his last major appearance at St Andrews as The Open is not due to return there until 2026. 

"I'm not retiring from the game," the 46-year-old Woods, winner of The Open at St Andrews in 2000 and 2005, said.

"But I don't know if I will be physically able to play back here again when it comes back around.

"I'll be able to play future Opens, yes, but in eight years' time, I doubt if I'll be competitive at this level."

The winner of this year's tournament is set to receive a record prize of $2.5 million (£2.1 million/€2.5 million).

This is part of a substantial 22 per cent rise on last year's prize fund, which now totals $14 million (£11.8 million/€14 million).