Justin Thomas reads the fourth green during the final round of the PGA BMW Championship golf tournament at Medinah Country Club on Sunday in Medinah, Ill. (AP photo)

MEDINAH, Ill. — Staked to a six-shot lead, Justin Thomas spent more time Sunday worrying about what could go wrong than ending 12 months without winning.

And right when it started to go wrong, Thomas delivered his biggest shots in the BMW Championship.

In a span of three holes around the turn at Medinah, his six-shot lead shrunk to two. Thomas answered with two clutch wedge shots, two big putts and sailed to a 4-under 68 to secure a three-shot victory over Patrick Cantlay, who gave him a battle to the end with a 65.

“Patrick played unbelievably, put a lot of heat on me,” Thomas said. “In the end, it could have been good for me. It kept me focused, kept my head down. … I was really nervous going into today. I remembered that it’s really hard to win a golf tournament, and I’m glad that I was able to do so.”

The timing was ideal.

His first victory since the World Golf Championship at Firestone last year moved him to the top of the FedEx Cup going into the Tour Championship, where he will start the tournament at 10-under par with a two-shot lead under the new scoring format as the final 30 players chase a $15 million first prize.

“I can certainly say I never slept on a Wednesday lead,” Thomas said.

Cantlay, who made four straight birdies around the turn, secured the No. 2 position and will start at 8 under. Brooks Koepka will be 7 under, a staggered start all the way down to even par for the final five players.

That includes Lucas Glover, who went bogey-double bogey until finishing with a two-putt par from 40 feet to secure his first trip to the Tour Championship in 10 years.

It will not include Masters champion Tiger Woods, the defending champion.

Woods was a long shot going into the final round to crack the top 30, and he closed with a 72. East Lake was his first victory in five years, capping his return from four back surgeries, a special moment replaced some six months later by his Masters victory.