There are no guarantees that the waterlogged course will be playable, meaning the event may be reduced to 54 holes, which Rose would win with a 17-under-par total of 193.
The venerable Philadelphia course has been turned into a virtual pitch and putt by the best players in the world, the product of wider-than-normal fairways and a course softened by an abundance of rain at the BMW Championship. The greens are fine, the bunkers are going to be fine.
Rory McIlroy currently sits on 16-under par at the event, now just one shot behind leader Justin Rose after the Northern Irishman produced another scintillating round of 63 on Saturday to go with his opening 62.
The plan is for groups of three to begin play at 7:30 am EST off two tees at a time.
"We will do everything we can to play tomorrow but we'll just see what Mother Nature gives us", PGA competitions vice president Carlton "Slugger" White said.
Under tour rules, half the field must complete the final round by Monday for an event to extend into Tuesday.
Finally, Bill Haas, who has played a part in three winning Presidents Cup teams, might have been a decent shout for a Ryder Cup spot not too long ago but the 36-year-old has missed 10 cuts in 22 starts in 2018, leaving Furyk with a hard choice between Schauffele and Finau on Monday.
Schauffele, hopeful that a victory will give USA captain Jim Furyk reason to pick him for the Ryder Cup, stayed with Rose the whole way until his lone bogey on the 18th for a 67.
At stake is chance for Rose to reach No. 1 in the world for the first time with his third title in the Philadelphia area, including his U.S. Open at Merion five years ago.
Keegan Bradley made two tough pars for a 66 and narrowly edged past Spieth for the 30th spot.
Projected 51st, Adam Scott would not make it to the Tour Championship. The 14-time major champion should play in weather-delayed tournaments more often, apparently. Players will be in threesomes off the first and 10th tees to try and avoid a Monday finish. If he doesn't qualify, Spieth would violate a recent policy requiring PGA Tour members to play a tournament they haven't been to in the last four years.
"I could start to feel the weather coming in and getting darker".