Jason Day and Brendon Todd share a one-stroke lead on a congested leaderboard after the first round of the US PGA Championship on Thursday.

Day, the 2015 champion, carded a bogey-free five-under 65 at TPC Harding Park in San Francisco.

The Australian capitalised on favourable early conditions and made five birdies to sit a stroke clear of nine players, alongside Todd.

Todd produced the best round of those in action later in the day, although he mixed seven birdies with two bogeys.

Bidding to win a third straight US PGA title, Brooks Koepka is among that group after shooting a four-under 66.

Koepka mixed six birdies with two bogeys as the American continued to grow in confidence after a runner-up finish at the WGC-FedEx St. Jude Invitational.

Martin Kaymer, the 2010 champion, Scottie Scheffler, Xander Schauffele, Bud Cauley, Zach Johnson, Justin Rose, Brendan Steele and Mike Lorenzo-Vera are also in a tie for third.

Rose was just one under with six holes to play in his round, but the Englishman managed three birdies to be in contention.

In action for just the second time since the PGA Tour season restarted in June, 15-time major champion Tiger Woods opened with a two-under 68.

The American was even through his first 12 holes before a strong finish saw him birdie three of four holes prior to dropping another shot.

Bryson DeChambeau accidentally broke his driver during his first round and was twice four under, but finished with a 68.

Dustin Johnson carded a one-under 69 to be tied for 33rd, a shot better off than four-time major champion Rory McIlroy, who battled to his 70.

Jon Rahm also struggled to get going on his way to a 70, while 2017 champion Justin Thomas fired a 71.

Jordan Spieth's hopes of completing a career Grand Slam this year took a hit, the American again battling as he opened with a 73 that included five bogeys. Rickie Fowler also shot an opening-round 73.