After picking up two strokes on the front nine, Young caught fire coming in at Albany Golf Club in Nassau in the Bahamas.
He birdied 10 and 12, then picked up five strokes in the space of four holes with a birdie at 14 followed by an eagle at 15 and birdies at 16 and 17.
He was tied on 10-under 134 with Japan's former Masters champion Hideki Matsuyama, reigning US Open champion J.J. Spaun, former US Open champ Wyndham Clark and Akshay Bhatia.
Young said he was "fortunate" to chip in for eagle at the par-five 15th, calling his late surge "one of those little stretches where I had some tap-ins and then made a couple, too."
"Just ended up being a big string of good holes," said Young, who gave back a stroke with a bogey at the last.
He said his game was not very different from Thursday, when he signed for a two-under.
"I feel like I played pretty similarly and just made a couple (of) putts down the stretch," said Young, who claimed his lone PGA Tour title at the Wyndham Championship this year and was a captain's pick for the US Ryder Cup team.
Matsuyama had six birdies without a bogey in his six-under 66. Spaun, Clark and Bhatia, who were all part of a five-way tie for the overnight lead, each carded four-under 68s.
World number one Scheffler, who was among the first-round leaders, had an eagle and a double-bogey along with four birdies and a bogey in his three-under 69.
"I think I did some good things out there," Scheffler said. "Just a few too many mistakes, but overall still felt pretty good."
While Scheffler is going for a third straight victory in the unofficial 20-man event hosted by Tiger Woods, he said it offers less of a chance to build momentum for the upcoming season than to assess where his game is after his post-Ryder Cup break.
"I think you can always take good momentum from playing well (but) I wouldn't look too far into it if I didn't have a good week this week," he said.
"Overall I feel like it's a good place to kind of see where my game's at and then kind of get ready for the season."
Woods, a 15-time major champion, is not playing in the tournament, saying on Tuesday that the recovery from his latest back surgery is "not as fast as I'd like it to be".