Xander Schauffele struck six successive birdies en route to a superb second round of 64, establishing a three-shot lead at the midway point at the CJ Cup at Shadow Creek in Las Vegas.
Beginning on the 10th, Schauffele played his outward nine in a scintillating 29 strokes, parring only the 1st and 3rd hole and birdieing the rest, unleashing a stunning streak of six-in-a-row from 4-9.
A sub-60 round appeared a possibility at that stage but his back nine was prosaic by contrast, with just birdie on the 12th, parring the rest as he carded a course record 64.
First round leader, England's Tyrrell Hatton, on a high after his win at Wentworth, sits in second, three strokes off Schauffele.
Hatton could not quite match his first round of seven-under 65, but still managed to card a four-under 68 to be 11-under par. The 29-year-old had an eventful day, with seven birdies offset by three bogeys.
He carried on from his two-shot overnight lead with birdies on the fourth, seventh and eighth, to turn in three-under 33 and a formidable 10-under for the tournament.
In unusual scenes, Hatton had to re-situate his ball in a greenside bunker on the 11th after playing partner Jon Rahm's divot landed on it. He chipped out to eight feet but took two putts for bogey.
He recovered with birdie threes on the 12th and 14th holes, before ending with a run of bogey-bogey-birdie-birdie.
Lying third, a shot behind Hatton, was American Russell Henley, while England's Matthew Fitzpatrick was seven shots off the lead on seven-under.
The Irish duo are well back in the field, Rory McIlroy sitting at two-under after a second round of 69, while Shane Lowry sits at two-over par after rounds of 72 and 74.