SPRINGFIELD, N.J. — Minutes after finishing an opening-round 65 at the PGA Championship on Thursday, Jimmy Walker was asked what the biggest challenge was on the Baltusrol Golf Club course. Walker didn’t hesitate.

“The heat,” said the 37-year-old who lives in Boerne, Texas, and led the tournament for much of the day. “The wind wasn’t blowing, so it was always kind of hot. Just constantly sweating, couldn’t quit sweating, nothing to cool you off.”

It ranged from 95 to 98 degrees — with a heat index approaching 120 — much of Thursday as 156 professional golfers lathered on sunscreen, donned caps and short-sleeve shirts, and chugged fluids to stay hydrated.

And they all wore pants.

In fact, in the grips of a heat wave that has reached temperatures of 100 degrees — with a “feels-like” of 140 — it’s been easy to spot the professional golfers amid just about any other group of people since they descended on these generally leafy grounds Monday: They’re the guys in pants.

“If you ask me, it’s too hot for pants,” said a dripping John Daly as he walked off the course Monday, the week’s hottest day. As he is wont to wear, an eye-stinging technicolor tapestry draped his legs. He said he wished they stopped at the knees. “I’ve always thought we should be able to wear shorts, at least in practice rounds and pro-ams.”

Actually, it’s not entirely clear they can’t.

The PGA of America, which puts on the PGA Championship, said the event has no written requirement of pants, but historically has adhered to the rules of the PGA Tour, which oversees the largest American golf tournaments — and the conduct of those who play in them.

Here’s the Tour’s dress code, such as it is: “APPEARANCE OF PLAYERS: Players shall present a neat appearance in both clothing and personal grooming. (No objections appear to have been filed against the heavily bearded Andrew “Beef” Johnston.) Clothing worn by players shall be consistent with currently accepted golf fashion. The Tournament Director shall interpret this regulation, subject to the approval of the Commissioner.”

No one has ever interpreted those words to permit a bare male-golfer’s legs, groomed or not, to breathe fresh air on the course from Monday of tournament week until the final putt is holed, said Joel Schuchmann, director of communications for the PGA Tour.

“It would be fair to say there have been discussions but certainly nothing beyond that,” Schuchmann said earlier this week. “When players come to us with ideas or concerns, we always discuss them.”

The question of shorts reached new heights earlier this year when the European Tour decided to allow shorts at the HSBC Golf Championship in Abu Dhabi. The decision followed lobbying by salt-and-peppered veteran players such as Ryder Cup captain Darren Clarke, and it has been cheered by the younger stars, such as Rory McIlroy and and Jordan Spieth, both of whom donned short trousers in the UAE.

As far as I can tell, only one male player has ever deigned to get leggy in a professional American event, and that was a one-hole protest from Forrest Fezler in 1983.

Caddies have been allowed to wear shorts since 1996 — and thank goodness, said G.W. Cable, a caddie of some 10 years who this week is humping Chris Kirk’s bag. “I’m from Jupiter, Florida,” said Cable. “I like the heat. I’d rather be hot than cold. But this is shorts weather.”

Meanwhile, professional women routinely bare their legs in competition, although it’s possible there’s an aesthetic distinction there, as several male golfers have said, men shouldn’t be allowed to sport shorts.

Count Jimmy Walker, sweating in black slacks and bemoaning Thursday’s oppressive heat, among them.

“I think we all look good in pants. Some of us probably wouldn’t look as good in shorts.”

The issue likely will fade as the tournament progresses. Most forecasts call for highs in the lower 80s following rains Thursday evening.