Rory McIlroy struggled on his return to Kiawah Island with a three-over-par 75 in the opening round at the US PGA Championship as playing partner Brooks Koepka impressed.

McIlroy won by eight shots the last time the PGA Championship was staged at Ocean Course in South Carolina in 2012 and was installed as the favourite of many after ending a winless streak of almost two years at the Wells Fargo Championship two weeks ago.

However, the four-time major champion – seeking a first major title since 2014 – landed his very first shot into the water on a windswept morning before recovering somewhat with back-to-back birdies on Thursday.

McIlroy – a two-time PGA Championship winner – was level par at the turn after dropping another shot on the par-five 16th, but he managed just one more birdie compared to five bogeys as he closed for 75, eight shots behind Corey Conners.

Koepka played down expectations heading into the tournament due to a knee injury and he started slowly with a double-bogey on his first hole, though the two-time PGA Championship winner recovered well with two birdies in the next three holes.

After turning in 36, Koepka picked up three shots in four holes on the front nine to complete an impressive turnaround that saw him earn a share of the lead before Conners soared to the summit as he aims to add to his successes in this event in 2018 and 2019.

"I felt like an idiot," he told Sky Sports Golf when reflecting on his cagey start. "It was probably a poor club choice off 10. I thought three-wood would have carried, but it didn't. I also didn't find the face, it barely hit the face!

"The first rule is, if you're in trouble, get the hell out. I couldn't reach the green and it was a bad lie, so I didn't know where I was going. I just tried to hit a sand-wedge up by the green instead of just chopping it out.

"So it was a mental mistake there, and I deserved every bit of that double-bogey. But it kind of helped me refocus. I can't play with any mistakes, maybe one a day, and that was my one, and I got it out of the way on the first hole."

Koepka is joined on three-under par by former champion Keegan Bradley, Viktor Hovland. Aaron Wise and Sam Horsfield.

Bradley's opening round included four birdies and just one dropped shot, coming on the par-four 13th, while Hovland bounced back from an opening bogey with four birdies.

Collin Morikawa is one shot further back after bogeying his final hole, the defending champion joined on a first-round 70 by Martin Laird, who was also let down by a couple of dropped shots on his final two holes.

Justin Thomas finds himself way down the standings, meanwhile, after carding a three over that included a double-bogey on the 18th, while US Open champion Bryson DeChambeau had a mixed first day as he posted a level-par 72.

World number one Dustin is among the late starters, along with Jordan Spieth, Tommy Fleetwood and Justin Rose.