World number two Jordan Spieth made his move on Friday at the PGA Championship, carding a second-round 67 to move to six-under-par.
Spieth climbed to within one shot of leader David Lingmerth, who was the early pacesetter in the second round at Whistling Straits.
World number one Rory McIlroy fired his second 71 to sit on one-under, five shots back.
Starting at the tenth tee, Spieth birdied the 11th before giving that stroke right back at the 12th. It would prove his lone blemish of the day, while he added further birdies at the 16th and 18th to take the turn in 34.
On his closing nine, Spieth added birdies on the first, third and sixth holes to finish on five-under for the day and six-under overall.
While Spieth was superb, McIlroy, who was playing alongside the 22-year-old, struggled to get going a bit more, with an eagle at the par-five second, two birdies and a double-bogey at the 18th – his ninth hole – the Ulsterman's scoring on the day.
Lingmerth began the day one shot back from first round leader Dustin Johnson and carded an eventful two-under par 70, which included eight birdies, four bogeys and a double-bogey.
Johnson tees off in the afternoon session, along with other contenders the likes of Jason Day and Justin Rose, while Tiger Woods will be bidding to avoid missing yet another cut.