OAKMONT, Pennsylvania (Reuters) - Ernie Els speaks from experience when he says that this week's U.S. Open at fabled Oakmont Country Club will prove to be a survival test.

The strapping South African with the silky swing, who is nicknamed "The Big Easy", won his maiden major and first U.S. tournament title in a 20-hole playoff over Scotsman Colin Montgomerie and Loren Roberts at the 1994 U.S. Open at Oakmont.

Oakmont has changed over the decades, said four-time major winner Els, but the fast-running layout outside Pittsburgh hosting its record ninth U.S. Open remains a daunting challenge.

"Winning here at this unbelievably historic venue is quite something. It's almost like you win an Open Championship, you want to win it at St. Andrews or Muirfield," Els, 46, told reporters on Tuesday.

"When you win a U.S. Open, Oakmont is one of the iconic venues."

There are 50,000 fewer trees than when Els triumphed here, altering the look of the layout, and deep thick rough punishes errant tee shots. The fast, sloping greens can still confound the game's best.

Noting the passage of time, Els recalled how "a lot of us were still using wooden drivers back in '94 ... and it's amazing how the golf course has also changed.

"You could definitely move the ball out of the rough on to a lot of these greens. Nowadays, you can't really do that.

"I don't know what kind of chemicals they put in that grass, but it's growing. So that changed a lot."

MUSCLING THE BALL

Els, playing in his 24th U.S. Open, recalled that back in 1994 he was able to muscle the ball out of the rough toward the greens.

"Now it's at least a half a shot penalty. You try to get a wedge out to where you can play your next shot from. That's just the way it is," said Els.

Yet Oakmont is essentially the same treasured test.

"The holes itself, your strategy on the holes even, (despite) today's equipment and stuff that we use today, it's really similar," the South African said.

"They've moved some tees back, but you're hitting it into the same position as we did in '94. That's what I love about Oakmont ... they've saved an absolute iconic venue. It hasn't got too short. It definitely never got too easy.

"So this has just stood the test of time."

Els said the thick rough would "stymie" current players who have come to use hybrids to advance the ball out of rough.

"This is going to test the boys this week, I promise you," he said. "Of the four rounds you're going to play, at least one, maybe two is going to be a survival test.

"You're going to have stretches where you're going to have to try and survive, and it's going to happen to every player in the field."

"That is why this is the ultimate U.S. Open test at Oakmont ... mental, physical, everything. So you're probably going to need a couple of days off after Sunday."

Els will tee off with 2003 U.S. Open winner Jim Furyk and Oakmont's 2007 winner Angel Cabrera of Argentina in the first round on Thursday.

(Writing by Larry Fine in New York; Editing by Mark Lamport-Stokes)