Jordan Spieth in the thick of the action at top of packed British Open leaderboard going into final round

Jordan Spieth surged through a gridlocked British Open leaderboard as a third straight major title loomed large, but he had to share the spotlight with Irish amateur Paul Dunne at St Andrews after a remarkable day’s action on Sunday.

The 21-year-old American, bidding to become the first man to win the year’s first three majors since Ben Hogan in 1953, began the delayed third round in the chasing pack and lost ground early on but he stormed home with a seven-birdie, six-under 66 for an 11-under total, one off the lead.

Dunne, a year older but inhabiting a different golfing planet to Masters and US Open champion Spieth, ended a crazy day of low scoring in a three-way tie at the top on 12-under par 204 with Australian Jason Day and 2010 British Open champion Louis Oosthuizen.

Clearly on course for the amateur’s silver medal after a nerveless 66, Dunne remains in serious contention to become the first amateur to win the British Open since Bobby Jones 85 years ago.

At this most unusual of Opens, anything seems possible,

With flags hanging limp like damp tea towels – a huge contrast to Saturday’s gales that wiped out the third round and forced a first Monday finish since 1988 – an eclectic mix of major winners, amateurs and nearly-men tucked into the Old Course birdie banquet with relish.

There were 37 sub-70 rounds, although the one notable exception was Spieth’s fellow American Dustin Johnson, the overnight leader, who collapsed to the day’s second-worst round, a miserable three-over 75.

Spieth struggled to make much headway early on and was clearly getting frustrated when he dropped a shot at the ninth.