As the top-ranked Scheffler went backwards with a one-over-par 71, Smalley carded a 69 to jump to four under for the tournament as the Philadelphia chill and Aronimink Golf Club continued to bite the game's best players.
Fellow American Chris Gotterup had enough Jersey toughness to handle the cold wind and treacherous greens, closing with three-straight birdies on Friday for five-under 65.
The low round of the tournament thrust Gotterup to three under as South African Aldrich Potgieter, one of seven first-round co-leaders with Scheffler, led the way midway through his second round.
Potgieter picked up two shots through the first nine holes to move to five under.
Former Masters winner Hideki Matsuyama shot 67 in his quest for a second major.
The Japanese superstar was alongside Gotterup at three under, the same score as Australian Min Woo Lee and Germany's Stephan Jaeger midway through their second rounds.
At just 21, Potgieter is looking to become the youngest golfer with a 36-hole lead at a major since Tiger Woods' historic win at the 1997 Masters.
Aronimink is plenty difficult without dealing with blustery conditions that made it feel colder than the low 50s (10s Celsius) for so much of the morning.
"Today would definitely be one of those days where I would be on the couch and I would be like, 'How did he hit it there?' and 'How did he do this?' And then you're out there, and it just feels like it's impossible," Gotterup said.
Gotterup has three PGA Tour titles since July, two of them this year to reach No.10 in the world. He had his best stuff on a stage that is the closest course to a home major. He grew up 100 miles away and played college golf at Rutgers, just up the New Jersey Turnpike.
Defending champion Scheffler, who had a share of the 18-hole lead for the first time in a major, did not find a fairway until his ninth hole.
One day after hitting 13 of 14 fairways, he didn't find the short grass until the 18th hole. He started on No.10 and already had three bogeys — all from the rough — through four holes.
He might have saved his round on the par-3 14th when he hit a beautiful lag putt from 80 feet for a two-putt par. That settled him, and he closed with an up-and-down birdie on the par-5 ninth to finish at two under and still well in the mix.
Two-time PGA champion Justin Thomas had another remarkable bogey that could have been much worse early in his round and was on the ropes until he steadied himself with a pair of birdies and salvaged another 69.
Thomas was playing with Cameron Young, who worked for pars and finished with an 8-foot eagle putt that gave him a 67.
Rory McIlroy and Bryson DeChambeau had afternoon tee times.
But the worst of the weather looked like it might be in the morning. Dustin Johnson, with perhaps his final invitation to the PGA Championship, ground out an even-par 70. Heading to the parking lot, he looked at a clearing sky and slightly calming wind and shook his head.
"It was blowing 100 for us," Johnson said with a grin.
The former world No. 1 and two-time major winner is not typically prone to exaggeration. But it was hard work out there.
With AP
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