McIlroy entered his second round with ground to make up after shooting a three-over 74 on Thursday.
He hit only four of 14 fairways in his first round and, according to PGA Championship Radio Sirius XM, he had been unable to use his usual driver because it was deemed to be non-conforming during testing by the United States Golf Association earlier this week.
The radio station reported that the decision did not mean McIlroy was at fault or even aware of the issue. They also said the USGA said testing results were kept confidential unless the player wanted to make it public.
The early signs in round two were better, a 15-footer dropping for birdie on the second hole, while three more shots were gained around the turn as McIlroy improved to one under par.
However, all of the breathing room he had earned ended up being required during a testing back nine.
An excellent par save on the 13th stopped the rot after two straight bogeys, before birdies on the next two holes restored a gap to the cut line – which was hovering between one and two over par during the latter stages of the second round.
There was some late drama as, heading down the 18th at level par, McIlroy pulled his tee shot left and his ball ricocheted off a hospitality tent before landing close to the water hazard.
But he recovered to make a bogey five, confirming his spot in the final two rounds.
Schauffele had found himself in trouble following two bogeys on the front nine but fought back sufficiently to extend his stay in North Carolina.
