Peter Malnati and Brian Harman lie alongside McIlroy at six under, while world number two Justin Thomas is three shots off the lead at four under. "I really struggled with my swing yesterday and I kind of got some good breaks", he said.
"But it's good that there's good signs". "I feel like the work that I did over the weekend sort of started to pay off already".
"If I can put the ball on the fairway and hit my irons as well as I have done the first couple of days I'll give myself a lot of chances for birdies and it's just about converting them and taking your opportunities". That was despite missing a few between 10 and 15 feet and there was also one missed putt from inside four feet.
"You never want to miss a cut in a Major, but it might have been a blessing in disguise for the rest of the year", he said.
But he was not carried away by one good day.
However, it was a day to forget for American Jordan Spieth, who started the second round in a tie for the lead, fell to a second round 73 to leave him on four under, three behind McIlroy and six off the leader.
The out-of-bounds to which he referred was at the par-five 13th, where he ran up an ugly eight after compounding his wild tee shot by finding a pond with his fourth. "But it was actually a pretty tough shot there, nearly a little downslope and I had to hit close to the ball, which you just have to commit to it".
Meanwhile, Australian Scott Hend fired a sensational 67 in windy conditions to lead the BMW International Open by a stroke from Qualifying School graduates Nico Geyger of Chile and Sweden's Henric Sturehed on six-under. I made a good shot on 11, our second hole, made the putt, making a solid par putt on 12, and then that freed me up a little bit.
US Open runner-up Tommy Fleetwood squeaked over the cut line on four-over after a second successive 74, but The Island's Paul McBride missed the cut by three strokes after a 75. I came off, I think, a third at Muirfield before the US Open, and maybe a second at Colonial to a second and a third, and the Open previous year off of a win here.
McIlroy birdied the opening two holes and grabbed three-in-a-row from the 13th onwards, but he missed out on joining Spieth and Johnson in setting the pace after a bogey at the last.
Kiwi golfer Danny Lee has given himself a shot at a top-10 finish at the Travelers Championship on the PGA Tour.
The 2006 East of Ireland victor (32) double-bogeyed the 16th and bogeyed the 17th, carding a three-under 69 to tie with Young on 11-under before losing out at the first extra hole. Defending champion So Yeon Ryu, coming off a victory Sunday in MI, shot a 67.