Scheffler, last year's Masters winner, dropped his approach inches from the hole at the first and sank a nine-foot birdie putt at the second to seize the lead at Oak Hill on five-under-par after four holes.
Fellow American DeChambeau, the 2020 US Open champion who has made the break to the Saudi-backed LIV golf circuit, fired a four-under-par 66 in Thursday's opening round to grab the 18-hole lead but was among the last to begin his second round on the formidable layout in windy and rainy conditions.
World number 11 Hovland, seeking his first major title, made birdie putts from just outside 10 feet at the first and just inside 20 feet at the second to match DeChambeau on four-under before falling back with a bogey at the third.
Canada's Corey Conners was also on three-under, one stroke ahead of 2011 PGA Championship winner Keegan Bradley with England's Justin Rose and Canada's Taylor Pendrith in the clubhouse on one-under 139 for 36 holes.
"Best putting day I've had in a long time," Pendrith said of shooting 69. "If I had an average or bad putting day, it could have been ugly. Definitely kept me in it."
Rose, the 2013 US Open champion, sank a 15-foot birdie putt at the 10th, sank a 26-footer for birdie at the 12th and made another from just outside 20 feet at 16 to launch his second round.
But the 2016 Rio Olympic champion stumbled with bogeys at 18, six and seven to shoot 70.
Rose, a winner in February at Pebble Beach for his first triumph since 2019, has 11 top-10 major finishes since capturing his only major title a decade ago at Merion.
"I think it went pretty well," Rose said. "Golf course was tough today. This is just going to be four days of kind of getting the most out of each day."
World number one Jon Rahm, the reigning Masters champion from Spain who opened with a 76, made a six-foot birdie putt at the second to reach five-over, right on the projected cut line.
Reigning US Open champion Matthew Fitzpatrick of England, who also opened on 76, was just over the expected cut line.
Four-time major winner Rory McIlroy, chasing his first major victory since 2014, shot a first-round 71 and began his second round with three pars.
Jordan Spieth, a three-time major winner trying to complete a career Grand Slam by winning this week, made a four-foot birdie putt at the second to stand on two-over for the tournament. The American is battling a left wrist injury.
Cameron Smith, the reigning British Open champion, fired a 72 Thursday and sank a 20-foot birdie putt at the second to stand one-over overall.
