Woods managed an eagle and seven birdies, his only hiccup being a 17th hole bogey before being joined in the lead by McIlroy.
The Northern Irishman capped his round of 10 birdies – with six in succession from the ninth hole – in the heatwave conditions on the Aronimink course.
McIlroy though let slip any thoughts of a 59 when he bogeyed his 16th and 17th holes.
Woods’ effort is the first occasion since capturing the 2013 WGC – Cadillac Championship he has shared the lead after any round on the PGA Tour.
Woods and McIlroy had played a 9-hole practice round together on Tuesday and with Woods packing two putters into his bag.
Upon deciding which one to use at the $9m event, he opted for the Scotty Cameron putter which won him 13 of his 14 Majors.
“I’ve been monkeying around with the Scotty Cameron back home and in the backyard, so it felt good,” Woods said.
“I’ve hit hundreds of millions of putts. I’ve had it since ’99. I’ve hit putts with it so my body just remembers it.
“I made a few putts today and also from right of the gate with birdies at 10 and 12 and 13 so that was a nice way to get things rolling.”
Woods had also ignited thoughts of his career-first 59 after an outward nine that produced a seventh-hole eagle and four birdies, and in the process recording just 13 putts, in a six-under par 29.
It is the sixth occasion in Woods’ 79 PGA Tour-winning career he’s recorded nine holes in 29 or better, and on four of those five prior occasions he has gone on to win.
Woods moved to seven-under par with a birdie at his 10th hole but then parred his next five holes ahead of a 16th hole birdie.
“I made some great putts out there today including getting off to a better start than I have most of the season,” he said.
“To shoot 29 on the front nine helps. It helped a lot.”
The effort also is Woods’ lowest round all season since a final round 64 to finish second in the PGA Championship while it is his lowest PGA Tour score since a second round 61 to capture the 2013 WGC – Bridgestone Invitational, and his last taste of success anywhere.
Woods clearly looked refreshed after electing not to visit the course on Wednesday, with the heatwave in Philadelphia causing much stress on the body.
“The heat is hard for me because I lose so much weight out here,” said Woods.
“I don’t eat enough calories because I drink so much water. Therein lies the issue. I lose so much weight and lose strength and I lose power and endurance.
“It’s a task. It always has been my entire year playing in hot conditions trying to keep my weight.
“So, that’s why I went to the gym yesterday, did some treatment and watched TV.”
McIlroy had been a shot clear of Woods at nine-under par after 15 holes when Woods headed for the clubhouse.
But bogeys on the seventh and eighth holes cost the World No8 posting a sub-60 first round.
“What was worst was probably just not giving myself a better chance to shoot the 59,” he said.
“I can accept bogies. Definitely I can accept a bogey on a hole like on the 8th hole and the bogey on seventh wasn’t good but you don’t get many opportunities to break 60 and today was one of them and I didn’t capitalize.”
American Xander Schauffele boosted hopes of securing next Monday’s very last spot into the USA Ryder Cup team to be in third place with a 63 while Rickie Fowler, who played alongside Woods, returned from injury to shoot a 65.