Phil Mickelson hits off the second tee on a soggy Sunday in Illinois
The battle for the BMW Championship will go into a fifth day after Sunday's play in Illinois was beset by bad weather.
Torrential rain left standing water affecting fairways and greens on the par-71 Conway Farms course in Illinois and twice forced the final round's play to be suspended.
Only four players had managed to complete their final round - Rory McIlroy among them - when the siren first sounded at 2pm BST to usher the field back into the clubhouse.
With overnight leader Jim Furyk not scheduled to start until after 10pm, organisers had already decided an extra day would be required before players finally returned to the course three-and-a-half hours later.
But further stormy weather halted the action again at 7.30pm to further increase the backlog.
It is the third unscheduled Monday finish on the PGA Tour this year, with 22 tournaments in total delayed by weather on the US circuit this season, including the first three FedExCup playoff events
McIlroy had signed off with a relatively promising three-under 68, given his recent form, but remained 20 shots behind a still-to-play Furyk.
American Furyk, seeking his first PGA Tour victory since the Tour Championship in 2010, was at 13-under overnight after carding a two-under 69 in Saturday's third round.
Steve Stricker sits a stroke back in second, having soared into contention with a 64, ahead of fellow Americans Brandt Snedeker (71), at 11 under, and Zach Johnson (69), at 10 under.
World number one Tiger Woods, still smarting after being docked two strokes for a rules violation during Friday's second round, is a further shot back in fifth after returning a third-round 66.