Final course fit for a king

So, waiter, Roger Federer would like to try something new for this evening’s Open-closing meal: an Argentine named Juan Martin del Potro.

Argentine steaks are famous throughout the world, but del Potro will be something different for the champion - the biggest slab of beef he’s encountered in dining on the lads raising a rumpus on the pampas. Del Potro, who ruthlessly stunned the struggling Rafael Nadal, 6-2, 6-2, 6-2, in one of yesterday’s semis, measures 6 feet 6 inches by 182 pounds. And the way he’s playing alerts Federer that, in this case, Argentine beef may not be so tender as advertised.

Del Potro’s hefty righthanded serve and ferocious groundstrokes (both hands clutching the backhand), pushed Nadal all over Arthur Ashe Stadium for 2 hours 20 minutes, never letting Rafa get comfortable. Though the third-seeded Nadal, ever the relentless competitor, constantly ran every which way like a little boy lost, he couldn’t prevent the worst major tournament defeat in his illustrious career.

Six games. A pittance. He held five break points, cashing none, admitting that his strained abdominal muscles wouldn’t allow him be the real Rafa.

“Sometimes when I serve the abdominal kill me, no?’’ Nadal said. “But it was important for me to play this tournament, to try my best. It’s one of the most important tournaments.

“And it was important for me to make semifinals, to confirm I came back the right way. The knees [tendinitis] are all right now. I can’t be very happy today, but at the same time I feel that I can really do a lot more.’’

But will he? He shouldn’t be declining at 23, but Rafa has given his body brutal usage.

Federer, behind a brief instant, 4-2, to Djokovic in the first set, zoomed beyond the Serb, 7-6 (7-3), 7-5, 7-5, in his 22d straight major semifinal. And if that isn’t phenomenal enough, he’s in his 21st major final, and has graced all four major finals for an unprecedented third time. Pursuing the ghost of Big Bill Tilden - US champ 1920--25 - Federer seeks his sixth straight title, and has won 40 consecutive matches at Flushing Meadows. Tilden’s streak was 42.

Although this is del Potro’s initial major final, Federer (6-0 against him) is wary - and should be.

“He’s getting better fast,’’ he said. “I had a difficult time with him in Paris [6-4 in the fifth], and I know he likes hard courts here better than clay.’’

A good-natured kid with a big smile and a scruffy sort-of beard who will turn 21 on the 23d, “Delpo,’’ as his friends call him, said, “This moment is so nice. I always dreamed of this moment [a major final]. It’s part of my dream that this is my favorite tournament, since . . . when I saw the stadium so big [2006, losing in the first round] and I say to myself this will be my favorite tournament.’’

His progress has been as sensational as his growth spurt that made him the tallest of all major finalists, and the first Argentine in the US title bout since Guillermo Vilas seized it from Jimmy Connors in 1977, the last championship match at Forest Hills. Delpo shot up from No. 159 in 2005 to No. 9 in 2008, and is now at No. 6.

He feels his serve and forehand are the key elements in his game, but he moves well on those long legs, and plays with an easygoing style that seems almost nonchalant.

“I have to play better - I’ve never beaten Roger,’’ he said. “The crowd, they help me to be happy on the court, you know. I heard the crowd so exciting when I did a good point, and that’s beautiful for me.’’

He dealt with Nadal’s mastery and mystery of spin confidently, flattening it out with deep groundies. His depth kept Rafa on the defensive and atypically downcast.

Federer, the new father, was in a jovial mood, and called his second-to-last shot “so, so rare.’’ Maybe even his greatest shot, a crowd tickler but certainly not the most important.

“I’ve done it three or four times,’’ he said of the “wicket’’ shot. Chasing a Djokovic lob with his back to the net, Federer overtook the ball and belted it blindly between his legs the length of the court for a winner - a dangerous shot for a guy unless he has the Federian touch. It took him to match point, quickly obtained.

Djokovic applauded. “I mean that shot, you saw the reaction of the crowd. What can I explain? I get the feeling he plays more relaxed in the last couple of years because now he’s married, a father, and broke all the records,’’ he said. “He wants to win even more and that makes him even more dangerous.’’

Djokovic said with a laugh, “In moments of frustration I just say, ‘Can somebody come and help me out. Let’s hit two against one or something?’ ’’

Will del Potro serve a frustration course to Federer? I think he has a chance.

Or will he be just be another tasty dessert for Roger at the end of US Title 6, his 16th major singles title?