Billy Horschel and Joseph Bramlett are co-leaders at five under after Thursday's opening round of the Honda Classic.

Horschel came into the event as the second-highest ranked player in the field, at world number 19, as many of the world's best opted to take the week off ahead of bigger prize pools at the upcoming Arnold Palmer Invitational and The Players.

Looking to capitalise on the weaker field, Horschel posted six birdies and one bogey during his first trip this week around PGA National in his home state of Florida. Meanwhile, Bramlett went bogey-free for his 65, joining Horschel at the summit after a birdie on his final hole.

Rounding out an all-American top-five are Pierceson Coody, Justin Suh and Carson Young tied for third at four under, and Young still has three holes to play after his round was cut short by fading light.

The only player in the field ranked higher than Horschel – world number 18 Im Sung-jae – is part of the logjam at three under that includes English duo Ben Taylor and Matt Wallace, while world number 20 Shane Lowry headlines the group one further back with Australia's Min Woo Lee.

Defending champion Sepp Straka made a safe start at one under, with last season's title the first and only of his PGA Tour career so far.