Will problem solvers continue to flourish at testing US PGA?

US PGA Championship second round leaderboard

The second day of the US PGA Championship crystallised what was already becoming clear: Aronimink is a course for the golfers who adapt the quickest.

Maybe there should be little surprise that Maverick McNealy, an intelligent but unheralded American who once considered snubbing golf for a business career, is leading the way.

Just like on day one, the majority of the world's leading players were again left befuddled and bemused by a punishing course set-up.

Those who were able to think strategically and problem solve were rewarded.

The later starters, including McNealy and Rory McIlroy, were also able to take advantage of slightly more benign conditions in the late evening sun.

McIlroy's pre-tournament prediction of being able to take the sting out of Pennsylvania course by smashing his driver as far as he could proved wide of the mark in a disappointing opening round.

On Friday, the Masters champion demonstrated his ability to reconfigure and bounced back with one of only two bogey-free rounds - a three-under 67 which left him one over par and five shots behind the leaders.

Given the volatile nature of this tournament, McIlroy knows the value of his unflustered round.

"It was a day to get back into the tournament and that's what I managed to do," McIlroy said.

McNealy, the son of a Silicon Valley billionaire, sits alongside fellow American Alex Smalley atop a bunched leaderboard which continues to feature some surprising names near the summit.

The pair are a shot ahead of Germany's Stephan Jaeger - who had an unusual round of 18 pars - and South Africa's rising star Aldrich Potgieter, although the presence of American Chris Gotterup, Japan's former Masters champion Hideki Matsuyama and Australia's Min Woo Lee - all in form on the PGA Tour this year - is far from leftfield.

Lurking below the frontrunners are a host of superstars eager to pounce at the weekend.

World number one Scottie Scheffler, fellow American Cameron Young and Sweden's Ludvig Aberg are in a group on two under par, while Spain's Jon Rahm is one under.

Three-time major champion Jordan Spieth - aiming to finally end a nine-year wait to complete the career Grand Slam - is alongside McIlroy at one over.

With 58 players all within six shots of the lead the second men's major of the season remains impossible to call.

More to follow.