Rory McIlroy and Brian Harman share the lead at BMW Championship

Rory McIlroy came up trumps despite opting for the road less travelled at the Olympia Fields North Course.

The Northern Irishman picked up five birdies without dropping a shot, while Champion Golfer of the Year Harman split six birdies with a bogey on the par four 12th.

Given McIlroy's wayward radar off the tee, he was surprised as everyone else to find himself at the top of the leaderboard after an adventurous round.

"Only hitting three fairways today and coming up with 65 is a bit of a bonus," said the world number two, as per pgatour.com.

"I'm not saying I was trying to aim for the rough. A lot of the tee shots I was just being super aggressive because I knew in the back of my mind I wasn't really being penalized for it.

"The golf course is certainly not playing the way it played in 2020. That was not my approach a few years ago here. But hopefully with the wind and the sun, the golf course starts to firm up a little bit and starts to play a little bit more like how I think it should play."

One passage of scrambling was particularly impressive from McIlroy. While he just had 116 yards left on the par-4 17th green, he was in the trees staring at the large bunker that protected the putting surface. He punched an iron through the trees, just over the bunker, went through the green, then chipped in for a birdie. Casual.

"There was a couple of branches above the window I was looking at, and I was like, 'If it hits those, it's just going to drop down near that front left bunker and I'll have a decent angle down the green and have a 10-footer or less to save par," he recollected.

"It was a bit of a hit-and-a-hope. Just trying to thread that needle. It was either chip it out or take it on. And it's only Thursday."

McIlroy and Harman lead by one from a six-strong chasing pack which includes England's Matt Fitzpatrick.

The 28-year-old dropped shots at the start and end of his opening round, but birdied six of nine holes around the turn.

Meanwhile, Patrick Cantlay has some improving to do if he is to be successful in his bid for a third-straight victory in the BMW Championship. The American carded a two under 68 on Thursday to sit equal-12th.