Augusta National is the pinnacle of golf — the course by which all others are measured.

So when a two-time Masters champion suggests the greens on the East Course at The Broadmoor are the toughest he’s ever played, that assertion carries some weight.

After Thursday’s first round of the U.S. Senior Open, it’s a claim dozens of others likely would stand behind. Even after several days of rain helped to soften those greens.

“Difficult.”

“Challenging.”

“Treacherous.”

Those were some of the early reviews. And they were made by players who fared better than most on the USGA setup.

“The Broadmoor may have the toughest greens anywhere, tougher than Augusta,” said Bernhard Langer, who won golf’s coveted green jacket in 1985 and 1993.

Jack Nicklaus, a six-time Masters champion who in 1959 won the U.S. Amateur on the East Course, has made similar comments.

So what is it about the greens that proves so difficult, challenging and treacherous?

Look no farther than the towering peak to the west: Cheyenne Mountain.

“Just the slope,” said Australian Mark Hensby, who made nine birdies but also six bogeys in a 3-under-par 67 on Thursday. “There’s so much slope, and it all comes off that mountain.”

Added American Ken Tanigawa, who suffered only one bogey on his way to a 68: “When the mountain is there, yeah, it’s a bit of a head-scratcher at times.”

Head-scratching is a nice way to describe some of the scenes that played out during the first round. Less than half of the field finished with a putting average of below 2.0.

For those hoping to make it to the weekend, it’s not so much about avoiding three-putts. It’s more about limiting them.

American Bob Estes carded a 68 that included a three-putt and several “good” two-putts. Stephen Gallacher of Scotland also had a 68, mainly by not getting “too greedy” with the flat stick.

“The greens are sort of the toughness of the golf course,” Gallacher said. “You’ve got to be switched on the whole time.”

They are greens that have stood the test of time, providing defense for a course that doesn’t intimidate with its yardage or its hazards.

“They’re very old school,” said Ireland’s Padraig Harrington, who shot a 67 to share the lead with Hensby. “And when you have those slopes in greens and they get them a little quicker with the heavy rough, it can be difficult.”

Sounds a whole lot like Augusta National.