Lingmerth, who had opened with a five-under-par 67 to trail overnight leader Dustin Johnson by one shot, drained a 24-foot putt at the par-four first and a nine-footer at the par-three third.
The Swede, who won his first PGA Tour title at the Memorial Tournament in June, then rolled in a 13-foot birdie putt at the par-five fifth to get to eight under overall.
That put him two strokes in front of Johnson, who was set to tee off later in the day, and three ahead of another American in Scott Piercy, who birdied his opening hole in the second round at Whistling Straits.
Also making early moves on Friday were Argentina's Emiliano Grillo, two under after 10 holes to trail Lingmerth by four, and Zimbabwe's Brendon de Jonge, three under for the day after 10 holes to get to three under overall.
The marquee grouping of world number one Rory McIlroy, second-ranked Jordan Spieth and British Open winner Zach Johnson was also out early on the links-style layout and experiencing contrasting fortunes.
While defending champion McIlroy and Spieth, bidding this week for a rare third major victory in the same year, were level for the day, Johnson was three under after making four birdies and one bogey in the first six holes.
McIlroy and Spieth were both at one under for the tournament with Zach Johnson a further stroke back at even par.
As was the case in the first round, the early starters on Friday were expected to benefit from calmer conditions at Whistling Straits before the winds begin to strengthen in the afternoon.
Among those who will be teeing off in the more difficult afternoon wave are first-round pacesetter Dustin Johnson and former world number one Tiger Woods, who struggled badly with his putting on the way to an opening 75.
Woods, who won the last of his 14 majors at the 2008 U.S. Open, has missed the cut in his last two majors and faces an uphill climb if he is to avoid a third in a row for the first time in his career. – Reuters
Original source: Lingmerth makes his move at PGA