NORTON, Mass. — Paul Casey looked at the leaderboard late in the third round Sunday and saw a lot more names in the mix than he realized. He took care of that with a 3-iron into 30 inches on the final hole for an eagle and a three-shot lead at the Deutsche Bank Championship.

Then he looked at the forecast, and realized his work was just starting.

Casey made birdie and eagle over his last three holes for a 5-under 66, giving him a three-shot lead over Brian Harman going into the Labor Day finish as he tries to win on the PGA Tour for the first time in seven years.

Only five players were within five shots of Casey, who was at 15-under 198.

Rory McIlroy (66) and Louis Oosthuizen (64), who staged a duel at the TPC Boston four years ago, were six shots behind. It was difficult to count out anyone with a forecast for 35 mph wind and burst of showers from the remnants of Hermine due in New England.

Starting times have been moved forward to give the tournament the best chance of finishing.

“I don’t think anyone’s completely prepared for tomorrow,” Harman said after his 66. “It’s more about survival and just doing the best you can.”

Harman will be in the final group with Casey and Smylie Kaufman (68), who was in the group at 11-under 202 along with PGA champion Jimmy Walker (70) and Kevin Chappell, who had the lead going into the back nine until hitting a tee shot into a divot that led to double bogey on No. 12. Chappell shot 71.

“To be sitting here at 66, I’m obviously over the moon,” Casey said. “Even with the great ball-striking, I found it difficult at the beginning, but to turn it around and have a lot of looks for birdies and make a few to come in, it’s been great.”

Chappell, still looking for his first PGA Tour victory, made a birdie at the 10th to get to 13 under until he went at the flag from the divot in the 12th fairway. He came up short in the hazard, tried to play out of the native scrub and went over the green and wound up with a double bogey.

“I said yesterday that at some point in time during the next 36 holes, I was going to be hit with adversity,” Chappell said. “Felt like I hung in there and finished with six straight pars from not-the-best position. So that’s what I’m going to choose to look at, and hopefully tomorrow I can get the ball in position and try to make some birdies.”

Casey made his at the right time, and his eagle at the 18th sent him home with a smile.

He had 232 yards to the hole with the wind coming out in and out of the left. The wind picked up and his caddie, John McLaren, stepped in and called him off. The wind died slightly, and the fun wasn’t over.

“It looked left,” Casey said about his shot. “And then the wind gusted and it went right. And after that, I was happy it got over.”

Casey was amazed by the low scoring, including his own, given the wind. The tour prepared for it by moving up several tees.

“A lot of guys were tearing it up,” he said. “Shows how good guys are out there.”

Casey has been through that before. Asked why he only has one PGA Tour victory — he has 14 on the European Tour, mostly recently the KLM Open two years ago — Casey pointed to his early years in the Tiger Woods era.

They seemed to play the same schedule, and Casey said that made it even tougher. And then there were the injuries, which slowed his career. Casey said he has had no excuses the last couple of years, and he was determined to change that.

All he has left is one more round, and what figures to be a day of nasty weather.

Dustin Johnson wasn’t among those in the mix. He was a birdie away from tying for the 36-hole lead on Saturday. Starting the third round just three shots behind, Johnson stumbled to a 75 and was 11 shots back. Jordan Spieth didn’t fare much better. He was five shots behind and had to rally with two late birdies for a 72. He 10 behind.

The top 70 in the FedEx Cup advance to the BMW Championship, which starts Thursday at Crooked Stick in Indiana. Casey was at No. 59 going into the Deutsche Bank, while Harman was at No. 67. Getting to the next FedEx Cup playoff event no longer is a concern.