After taking just 124 shots in total on the opening two days, Jason Day (AUS, -20) played a relatively unspectacular third round on Saturday. Despite this, the FedExCup leader still holds a comfortable advantage (six shots) at the top of the leaderboard.

Behind the PGA Champion, whose score is already four shots better than that of Zach Johnson when he won in Conway Farms two years ago, a fascinating battle for second place is brewing – and that is basically all the rest of the field is playing for, barring a complete breakdown from Day on Sunday.

Scott Piercy (USA, -14) has played his way into second place. Piercy carded a four-under round to pull level with the impressive rookie Daniel Berger (USA). One shot back is world number one and 2012 BMW Champion, Rory McIlroy. The Northern Irishman has carded just two bogies in the entire tournament so far – that is four less than Jason Day – but continues to struggle to convert enough of his birdie opportunities.

A trio of Americans are tied in fifth place on 12 under par going into the final round: Rickie Fowler, whose round of -5 was the lowest of the day, 2012 BMW Champion Dustin Johnson, and Kevin Na.

"Playing the way Jason is, there's not a whole lot we can do unless the tournament goes into seven, eight, nine, ten rounds," said Fowler. "There's another tournament going on, and he's in control of whatever he's doing. If he happens to come back, then we may have a chance."

As well as the win itself, another important scenario is being played out at the BMW Championship: only 30 of the 70 world-class players who teed off in Chicago will be rewarded with a ticket to the season finale in Atlanta. The battle for the positions around 30th place in the FedExCup rankings is a very close affair, with the decision set to go right down to deep in the fourth round. Proof of how quickly things can turn around came in the form of Piercy, whose projected ranking rose from 44th to 13th at the end of the penultimate round.