ATLANTA — A storm delay at the Tour Championship slowed the momentum of Brooks Koepka and Justin Thomas, right when they were starting to pull ahead in the chase for the $15 million FedEx Cup.

The final hour Friday showed how quickly it can change — and for Rory McIlroy, why no one is holding back in the season finale.

Koepka didn’t make a birdie on the back nine until the par-5 18th when he hit 5-iron from 239 yards to 8 feet behind the hole. He had to settle for a two-putt birdie, a 3-under 67 and a one-shot lead over Thomas and McIlroy at the tourney’s midway point.