A distant nine strokes off the pace overnight after narrowly avoiding a second successive missed cut in a major, McIlroy sank a 50-footer at the treacherous 17th, then chipped in from behind the green at the last to complete a three-under-par 67.
The Northern Irishman, who has been desperately searching for form and confidence during a poor season by his standards, birdied two of the toughest holes on the East Course to finish at three-under 207, five strokes off the early lead.
"To play like that on this golf course and do what I needed to do yesterday just to make the cut, and then to go out and play the way I did today ... it's been a good stretch of holes," said McIlroy.
"I've got another 18 to play, and hopefully I can just keep playing the way I am. It was good to feel the sort of rush again."
McIlroy's four-iron approach into the 18th ran through the back of the elevated green into thick rough, from where he struck a delicate chip and watched as his ball tracked down the slippery slope before disappearing into the cup.
"I couldn't have pitched a more perfect pitch," smiled McIlroy, who had pumped his fist in celebration before walking across to retrieve his ball from the hole amid loud cheers from the fans crammed around the green.
"I probably made up at least three, three-and-a-half shots on those last two holes."
SHORT GAME CLICKING
McIlroy, a double major winner, felt his short game beginning to click during last week's WGC-Bridgestone Invitational where he tied for 27th despite not being at his best off the tee.
"It was just a matter of trying to get a long game in shape," said the 24-year-old, who missed the cut at last month's British Open. "I wouldn't say that that was my best ball-striking round out there by any means, but I got it up and down when I needed to.
"And that was the most important thing," added the Northern Irishman, who has mainly struggled since switching his club brand at the start of the season to Nike in a lucrative deal reported to be worth $250 million over 10 years.
McIlroy, who coasted to victory by a record eight strokes in last year's PGA Championship at Kiawah Island, had not given up on his title bid this week, even after flirting with the cutline during the second round.
He finished strongly with four birdies over his final seven holes on Friday and knew he had to build on that in more challenging scoring conditions on Saturday as the drying East Course became faster and firmer in dazzling sunshine.
"I thought two 65s would still have a chance, so 10 under par," McIlroy said of his target over the weekend. "But the way the conditions are with the swirling wind, it's tricky out there.
"I felt like I still had a chance. Every time I'm in that position, I just think back to Quail Hollow a few years ago and what I did the weekend there."
McIlroy made the cut by a single stroke at the 2010 Quail Hollow Championship before shooting a 66 on Saturday and a course record 10-under-par 62 on Sunday to blow away a top-quality field by four shots.
"It gives me a bit confidence knowing that I've been in that position before and I've been able to win," he said.
"I know this is a major championship and it's a bit different, but I felt good enough about my game that I could go out there and post a good one today and at least give myself a chance going into tomorrow."
(Reporting by Mark Lamport-Stokes; Editing by Julian Linden)
