Making only his eighth appearance in a major, Jones sank a 15-foot putt at the par-four sixth before draining a 50-footer at the eighth on the way to a bogey-free seven-under-par 65 on a glorious sun-splashed morning by the shores of Lake Michigan.
That left him at 11-under 133 and two ahead of his compatriot Jason Day, who briefly held the outright lead at 10 under before he bogeyed the tricky par-four 18th to card a 67.
“I played great,” said journeyman Jones, a 35-year-old who won his first PGA Tour title at last year’s Houston Open.
“I putted really well. My speed on the greens has been really good.
“It’s amazing to be in the lead at a major. I’ve been in the lead on a Tour event, but a major’s a different story. I’m going to have fun with it. I’m pretty relaxed on the golf course.”
World number five Day, still seeking a first major title after several close calls, was pleased after recording seven birdies and two bogeys in the second round.
“I gave myself opportunities on the greens, didn’t really hit it close on 17 and 18, but overall I feel pretty happy with the position I’m in going into round three,” said Day.
England’s Justin Rose, among the 57 players still out on the course when play was suspended for the day on Friday after a thunderstorm rolled through the area, was at eight under after parring his final hole for a 67.
“Nice to wrap up the second round,” said Rose, the 2013 U.S. Open champion. “A bunch of birdies, which was nice. From today’s point of view, nice to finish with a strong par at the last.”
Much of the focus, however, remained on the remarkable Jordan Spieth who carded a 67 on Friday and was five strokes off the pace when the second round was completed as he bids to carve out another slice of golf history and join an elite club.
Masters and U.S. Open champion Spieth is seeking to join fellow Americans Ben Hogan and Tiger Woods as the only players in the modern era to win three majors in a single year.
Hogan was the first to complete the hat-trick, in 1953, and Woods followed suit in 2000.
“I feel good, I got a chance to win a major championship,” said Spieth, who fell agonisingly short in his quest to land the year’s first three majors when he tied for fourth in last month’s British Open, one shot shy of joining a playoff.
World number one Rory McIlroy, back in action to defend his PGA Championship crown after five weeks out due to an ankle injury, was at two under after carding a 71 on Friday.
Four-times winner Woods, however, plunged new depths when he missed the cut in a third successive major for the first time in his career after carding a one-over 73 in the second round.
The former world number one had left himself with plenty to do after putting poorly on the way to an opening 75 and despite improved play in the second round, he finished two strokes outside the cutline.
Also among those failing to advance were British Open champion Zach Johnson, 2013 Masters winner Adam Scott and Padraig Harrington, who clinched the PGA Championship in 2008.
(Editing by Ed Osmond)