Rory McIlroy was soaring through the PGA Championship's second round, one day after struggling to a three-over finish on the first day. He needed a strong performance on Friday and certainly delivered as the round progressed. Kicking off steadily, McIlroy soon hit a rich vein of form with three birdies across four holes from the seventh to the 10th, nudging himself under-par for the championship. With momentum swinging in his favour, he seemed set for an upward spiral. However, trouble struck when his tee shot landed in a bunker, which may have been caused by the fact he had to use a different driver, due to the USGA deeming his trustee one to be outside of competition guidelines. A 7ft putt stood between him and par salvation. McIlroy hovered over the crucial putt, the weight of the moment apparent. Yet, he pulled it left and was forced to watch his effort slide by the hole. McIlroy could be heard muttering: "Trust yourself, Rory," under his breath as he collected his ball, reports the Mirror US. This misstep was followed by another bogey on the 12th, extinguishing the fiery momentum that was just catching alight. Still, sparks flew from McIlroy's play with a brilliant bunker birdie on the 14th, then on the 15th, as he chipped in masterfully, demonstrating a short game that clung tenaciously to the competition. However, it was off the tee where he faced trouble again, including with his irons. He missed the green left on the Par 3 17th and couldn't manage to get up and down for par. Then he put his driver left on the edge of the creek on 18, leaving him needing a significant final putt to end with back-to-back bogeys, which left him right on the cut line and barely making it to the weekend. If only he had trusted himself on that putt on 11, things could have been quite different. But the swing in momentum was something he never managed to recover from, leaving him nine shots behind leader Jhonattan Vegas of Venezuela and with very slim hopes of repeating his Masters win. While McIlroy will be looking over his whole game before the final round, he will surely rue the USGA forbidding him from using his usual driver. NBC golf commentator Johnson Wagner admitted McIlroy was really unlucky. He said: "The USGA conducts these tests pretty much every week out here on professional golf. They test it across all aspects of the face of the driver. "Drivers fail all the time. Every single week somebody's driver fails and it is by no fault of the player, they don't know how to do it - it is a sophisticated testing system. "And when you're a player like Rory McIlroy that hits the ball as hard as he does the face naturally thins out...It's unfortunate that it happened the weekend of a major and that it maybe cost him a few shots yesterday...he did nothing wrong."