Marc Leishman hit two eagles in a 10-under round of 61 to take a commanding three-shot lead after the first day of the AT&T Byron Nelson in Dallas.
The Australian set out his stall early – holing a short putt for three at the par-five first and notching up two birdies in the front nine to go four-under at the turn.
A trio of consecutive birdies followed and his second eagle of the day came at the par-five 14th from a 13ft putt.
Speaking after the round to The Golf Channel, Leishman said: “I didn’t even think about 59, every other time I have been close to it I have thought about it.
“I didn’t get ahead of myself which was good. 61, I’ll take that.”
Two Americans, JJ Spaun and Jimmy Walker, sit on seven-under, the former carding six birdies in seven holes, but bogeying the par-four 15th.
A chasing pack of eight sit a shot behind that and tied for fourth, while Ireland’s Seamus Power is at five-under with 11 other players.
Northern Ireland’s Graeme McDowell carded a 67 to sit tied for 23rd, with an eagle on the par-five seventh cancelled out by dropped shots on the 9th and 18th.