An absorbing conclusion to The Open was in prospect as the leaders prepared to begin their final rounds at St Andrews on Monday.

Following four dramatic days of action - featuring two weather-enforced suspensions in play that led to the tournament continuing into a fifth day for the first time since 1988 - Paul Dunne, a 22-year-old amateur, shared the lead at 12 under with Jason Day and Louis Oosthuizen - the 2010 champion at this venue.

Jordan Spieth was a shot back and very much in contention for a victory that would put the 21-year-old one step away from an unprecedented Grand Slam, as well as securing top spot in the world rankings.

And a host of other players still had realistic hopes of lifting the Claret Jug on a cloudy and breezy afternoon in Fife, such was the congested nature of the leaderboard.

Two-time Open winner Padraig Harrington sat fifth at 10 under with 18 holes to play, one clear of a pack featuring Sergio Garcia, Justin Rose, Adam Scott and Zach Johnson.

Remarkably, Dunne - out in the final group with Oosthuizen at 2:30pm local time - was far from guaranteed to claim the Silver Medal for leading amateur, with Jordan Niebrugge among those at nine under and Oliver Schniederjans up to 10 under as he neared the end of his round.

With birdies again in plentiful supply, Luke Donald and Phil Mickelson also impressed in reaching 10 under on the back nine, but the latter then drove out of bounds on the 17th en route to a triple-bogey seven, his ball coming to rest on a balcony at the Old Course Hotel.