Rory McIlroy shot back-to-back birdies on the final two holes of his second round at the Tour Championship to card a three-under 67 and leave himself in a share of second place on 12-under, one behind world number one Brooks Koepka.

Koepka signed for a three-under 67 on day two, mixing four birdies - including a two-putt birdie on the par-five 18th - with a bogey for a one-shot lead in Atlanta.

Justin Thomas carded a round of 68 to sit beside McIlroy, who was in good spirits afterwards.

"I got lucky on 18," he told Sky Sports.

"I didn't hit a very good drive, and then I had a shot to get it up near the green with my second, and then once I hit that, I had a great lie for my third, and I just sort of rode my luck the whole way along that hole.

"Being three or four behind those guys for the most part of the day and then to catch JT (Justin Thomas) and only be one back of Brooks, it was nice to finish the way I did." 

The season-ending tournament uses an adapted sliding scale scoring format to decide the winner of the $15m FedExCup first prize, meaning Thomas started the week on 10-under, Koepka began on seven-under and McIlroy on five-under.

Koepka got off to a steady start in the second round, following up his first birdie on the par-3 sixth hole with two more in a row.

But a weather delay interrupted his momentum and it was only at the last hole that he was able to edge ahead.

McIlroy took better advantage of the 90-minute delay, firing his first birdie at the 12th before finishing his round with a 15-foot birdie putt on the 17th and a closing birdie on the 18th.