The 14-time major victor Woods and McIlroy have a one-stroke lead after both shot eight-under 62 which marked the American's best PGA first round since the 1999 Byron Nelson Classic.
Rory McIlroy keeps an eye on his shot.
"It was nice to make one like that up the hill to get things going", Woods told Golf Channel after the round.
Despite 18 major championships between them, the pair had never shared the lead after any round on the PGA Tour until they carded matching eight-under-par 62s in oppressive humidity on the Aronimink course, west of Philadelphia.
"I've been monkeying around with it at home in the backyard through the summer".
"I didn't make any putts".
It was the lowest score for Woods since he shot 61 in the second round of the 2013 Bridgestone Invitational, which he won by seven shots for his 79th title on the PGA Tour and 90th worldwide.
Turkey’s Erdogan warns against ‘bloodbath’ in Syria’s Idlib; calls for ‘ceasefire’
For his part, Rouhani demanded an immediate withdrawal by American forces in the country, which the other leaders agreed with. Putin said a ceasefire would be pointless as it would not involve Islamist militant groups it deems terrorists.
A Marcus Rashford Headbutt Undermines Manchester United Win
I for one am fully behind him and what he is looking to do at United at this current time. They say I'm in danger, but I don't think [I'm close to being fired].
Trump wanted Syrian president assassinated, new book by famed Watergate reporter claims
But after hanging up the phone, he told a senior aide: 'We're not going to do any of that. "We're going to be much more measured". Chief of Staff Kelly repeatedly calls Mr Trump an " idiot " and said that "it's pointless to try to convince him of anything".
Two days after he was selected by Jim Furyk as a Ryder Cup captain's pick, Woods chose to put his trusty Scotty Cameron back in the bag after he'd employed two other Taylormade flatsticks in play recently.
Xander Schauffele vaulted into the halfway lead as Rory McIlroy and Tiger Woods slipped back in the second round at the BMW Championship in Pennsylvania on Friday. Woods wound up with a one-shot lead that day and tied for seventh.
Six birdies in a row took McIlroy to the brink of that mythical score.
"Got off to a better start than I have most of the season". That's a stretch of 17 under par over 23 holes, even if only 14 of them counted in the tournament.
"It was one of those days where it was out there", McIlroy said. "Boy, shooting 29 on the front nine helps".
But a bogey at the first of those holes took the wind from his sails and he followed it with another at the hard 8th.
Woods was posing on his tee shot at the par-3 fifth, the sun glaring into him, and he couldn't figure out immediately where it went.
Woods birdied the first hole to get to seven under through 10 holes, then made five straight pars before feathering a wedge to inside a foot on No. 7.