Jab. Hook. Uppercut. Sucker-punch. Jordan Spieth and Rory McIlroy - clotheshorses both these days with their multi-million dollar apparel contracts; one dressed head-to-toe in UnderArmour, the other toe-to-head in Nike - traded punches of a kind in this second round of the 97th US PGA Championship here on the shores of Lake Michigan as if in a duelling world of their own.

Zach Johnson might as well have been a spectator, slowly, very slowly, going about his own business as if he were the gatecrasher at a prize fight. The British Open champion got lost in the crowd.

And when Spieth and McIlroy had finished for the day, one with the temperatures breaking into the 30s centigrade, it was the younger of the two sluggers who had delivered most blows. No knock-out, for sure, but Spieth’s 67 for 138, six-under, propelled him into the shake-up for a possible third Major title of the season, whereas McIlroy, who recovered from a horrible double-bogey midway through his round, fired a second successive 71 for 142 that kept him very much in the hunt.

A microcosm of their head-to-head came on the 18th hole, a Par 4 that has played as the toughest on the course. It was their ninth hole of the day and effectively the difference in their rounds came about here: from the fairway, McIlroy overshot the green into heavy rough and Spieth found a deep greenside bunker. And, from there, their respective journeys to the tin cup diverged.

For McIlroy, his ball nestled halfway into the tall grass with almost six inches between the actual ball and the ground, there came a recovery shot that failed to find the green. He ran up a double-bogey six. For Spieth, a holed-out bunker shot for a birdie. In a matter of moments, a three-shot swing between the two. All McIlroy could do was to stand by the edge of the green, his right foot positioned across his left and his left hand rested on his hips.

Two holes later, on the second, McIlroy was hitting a fairway wood from 256 yards into the greenside rough and chipping in for an eagle to repair that damage. Trading punches, like you’d expect from the world’s top two ranked players.

“We hate each other. It’s very challenging to talk to him,” quipped Spieth, with just the right note of sarcasm, afterwards.

“I’ve been friends with Rory since maybe middle to end of the first year that I was out here, when we first played together and whatnot. Obviously have a lot of respect. His game is extremely exciting. Watching him drive the golf ball is just inspirational. It’s unbelievable when he is hitting his driver good. I would argue there’s nobody like it when he’s hitting his driver good,” added Spieth, who would replace McIlroy as world number one with a victory.

And the warm handshake on finishing told its own story of a rivalry of mutual respect.

McIlroy - playing competitively for the first time since the US Open at Chambers Bay in June and recovered from the ankle ligament rupture that caused him to miss the defence of his British Open and WGC-Bridgestone Invitational titles - wasn’t, though, overly impressed with his own play.

“Maybe my iron play wasn’t quite as good as it was (on Thursday) . . . . I wasn’t very sharp around the greens (he said of scrambling). You’re going to have to have more of a short game to be able to salvage par sometimes. I wasn’t quite able to do that at points, but there’s still enough good stuff to give me encouragement and make me feel I can shoot a low one and get myself back into it,” said McIroy, defending a title he won at Valhalla last year.

McIlroy failed to kick on from his eagle on the second, didn’t birdie the Par 5 fifth and followed up a birdie on the sixth with a bogey on the seventh. It wasn’t the finish he wanted. “I’m not annoyed, I don’t feel that I should be annoyed, but just a little more disappointed with how I finished. ....it’s just being a bit more efficient, whenever you give yourself chances, take them, and be able to get it up and down when you put yourself out of position,” said the Northern Irishman.

Indeed, it would seem that McIlroy and Spieth are kindred spirits in their self-assessment. Although again getting into a position to again contend in a Major, Spieth - winner of the US Masters and US Open titles already this season - remarked: “ I’m still not pleased with the way I’m driving the ball at all. I’m hitting some quick draws when I’m playing a normal shot, which is weird. I haven’t had that really this whole year. So I was kind of just trying to guide the ball off the tee.”