Lowry is not getting ahead of himself with “such a long way to go”, but he is relishing the prospect of going out in Saturday’s final pairing after a second straight 67 hauled him level with JB Holmes on eight under par.
Tiger Woods bowed out although he salvaged some pride with a battling one-under 70, while McIlroy improved on his torrid opening 79 by 14 shots, but he still played one too many to extend his championship.
Lee Westwood roared into contention for an elusive maiden major title when he birdied four of the last seven holes to join Tommy Fleetwood on seven under, with Justin Rose adding to the strong English presence near the top of the leaderboard as he matched the 67s of his two compatriots.
Lowry’s previous experience of leading a major was a bitter one as he let slip a four-shot lead over the final round of the 2016 US Open and finished three behind Dustin Johnson, but he will start Open weekend as the fan favourite and could have had a commanding lead had he not faltered over the final third of his round.
The 32-year-old gave his supporters plenty to cheer early on when he birdied the opening three holes before converting further chances at the fifth and eighth as he stormed to the turn in 31, and he got another putt to drop at the 10th to open up a two-stroke lead over Holmes.
Lowry consolidated his position with a good run of pars before an erratic tee shot at 14 cost him his first bogey of the day and, with errors beginning to creep into his game, he had to dig deep to scramble pars before he chunked his approach to the last and bogeyed again to relinquish the outright lead.
“I’m obviously going to be thinking about it,” he said. “There’s no point in shying away from it. I’m in a great position but, my God, have we got a long way to go. There’s two rounds of golf left, on this golf course, against the best field in the world.
“The fans were incredible right from the first hole. When I holed that long putt on 10, it was unbelievable. You can’t help but smile and laugh at how it is. It’s an incredible feeling getting applauded on every green, every tee box. I’m out there giving my best, trying to do my best for everyone.”
Overnight leader Holmes looked on course to maintain his advantage when he birdied three of the first five holes, but dropped shots at nine and 14 either side of back-to-back gains added up to a creditable 68, ensuring he and Lowry would end the day one ahead of Fleetwood and Westwood.
Fleetwood was one of four players to go bogey-free on Thursday, but a poor tee shot at the first resulted in his first blemish before he responded with birdies at the second and fifth, and he picked up three shots in four holes after the turn only to give one back at the 16th.
However, he closed with a good three to get back to seven under, a score later matched by a resurgent Westwood when the veteran followed 11 consecutive pars with four birdies over the last seven holes, storming home in just 31 blows to revive his hopes of making his major breakthrough at the age of 46.
World No 4 Rose emulated the 67s of his two compatriots, including a superb eagle at the 12th, as he cruised to six under alongside young Aussie Cameron Smith (66) and South African Justin Harding (65).
But the top seven players on the leaderboard will doubtless be looking over their shoulders at major specialist and world No 1 Brooks Koepka, who is poised to contend for his fifth major win after a 69 lifted him to five under with Jordan Spieth, whose 67 kept him in the hunt for his first victory since lifting the Claret Jug in 2017.
Woods vowed to return for the FedExCup Play-Offs after his 70 was not nearly enough to avoid an early flight home, and McIlroy started the second day almost certain to join him following his Thursday disappointments.
But a more-relaxed McIlroy got the pulses racing when he made two birdies in a solid, outward 32 and then carded three in a row to begin the back nine, although he then dented his hopes when he bunkered his tee shot to the 13th, splashed out to 20 feet and left the putt short.
He launched a last-gasp rally with a birdie at 14 followed by a superb 230-yard tee-shot to eight feet at the 16th which he converted for his seventh birdie of the round, but he allowed too much break from mid-range at the 17th before pulling his second left of the target at the last to effectively end his tournament.