NEWTOWN SQUARE, Pa. — Justin Rose could sense the sky growing a little darker, the wind a little cooler and more brisk. Every shot means so much this time of the year, and the last two holes Saturday at the BMW Championship might mean even more.

Rose saved par from an awkward stance with his golf ball in the thick grass on the slope of a bunker. Xander Schauffele left a long putt from the tightly mowed collar on the 18th green eight feet short, and his par putt from there caught the high side of the cup and spun away.

When the third round ended, Rose had a six-under 64 — six birdies on the front, all pars on the back — for a one-shot lead over Schauffele and Rory McIlroy going into the final round at Aronimink, a course so soft from rain than the average score from 69 players over three rounds was 67.5

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 United States Open victory at Merion five years ago.

The question lingering amid the clouds: Would there be another round? Rose said he tried not to think about it.

“It was definitely in the back of your mind,” he said. “You could start to feel the weather coming in and getting darker. Kind of had the feel there’s some big weather coming. I said to my caddie, ‘How about tomorrow?’ Just got to get through today.”

Starting times were moved up to 7 a.m. Sunday with hopes that the heavy rain stays away, and that the final round can get in. The forecast is offering a small window Monday morning if needed. If the rain is relentless, there is a chance of the event’s ending at 54 holes, which has happened once in the 11 years of the FedEx Cup playoffs.

Rose was at 17-under 193, and 13 players were within five shots of him. That group included Tiger Woods, who missed only two greens in regulation, shot 66 and let a good round get away. That is how much of a pushover Aronimink has been this week.

McIlroy had a 63 with a double bogey, though he bounced back from that on the very next hole with a 3-wood that barely moved forward when it hit the green, caught the slope of a ridge and left a short eagle putt that he converted.

“I’ll be ready to play. I’ll be ready to go. I hope we play,” McIlroy said. “I feel like my game is in good shape and I’d love to get another crack at it out there and have a chance to take the lead.”

Rose made four straight birdies early on the front nine to quickly erase a two-shot deficit against Schauffele, and he finished the front nine birdie-birdie for a 29.

Schauffele, hopeful that a victory will give the United States 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.

“Still have a good chance tomorrow,” Schauffele said.

Jordan Spieth salvaged his round late again for a 66. He has never missed the Tour Championship, and he would probably face a penalty for not having added a new tournament to his schedule without competing in at least 25 events. He needs to be at East Lake in Atlanta in two weeks for the playoff finale, the Tour Championship, to reach 25. There is no tournament next weekend.

Keegan Bradley made two tough pars for a 66 and narrowly edged past Spieth for the 30th spot. For someone like Bradley, reaching the Tour Championship would put him in all four majors next year.

The scoring average, 67.17, was the lowest it had been all week. Only six players from the 69-man field were over par, and there was a 62 for the third straight round: the second straight such round for Tommy Fleetwood. After opening with a 71, he will go into the final round just two shots behind.

So will Rickie Fowler, who shot 65 despite a bogey on the final hole. Fowler played in the final group at Aronimink in 2011 when it held the AT&T National, though he faded to a tie for 13th. He is trying to win for the first time this year.

For Woods, it was another lost opportunity, even though he remains in the mix, five shots off the pace. He opened with two birdies, and the crowd was loud and on his side. He followed with 11 straight pars, even though he had chances from 15 feet and closer.

“I hit the ball well enough to shoot a low score and I got off to a quick start,” Woods said. “I was looking up on the board and everyone seemed like they were three under through eight, five under through nine. I was only two under par. I wasn’t doing much.”

It was the 17th time Woods had a 54-hole score of 198 or lower. The previous 16 times, he was leading or tied for second. At Aronimink, he was tied for 11th.