At opening day last Saturday at Donald Trump’s National Golf Club, The Donald was positively giddy with excitement.

“I think that when all is said and done,” he gushed, “this is going to be considered the best golf course in the state of New York.”

Was he being serious?

Better than Winged Foot, where numerous pro championships have been played? Better than the exclusive Westchester Country Club? Better than the Bethpage Black Course, which this summer became the first public course to host the U.S. Open?

“That’s right,” said Trump.No one would expect The Donald to do anything less than proclaim his new Westchester County course – which costs $300,000 to join – the best in the Empire State.

The long and tight, 7,200-yard tract in tony Briarcliff Manor has already gotten several positive reviews in the golfing press.

One thing is clear: Trump National has won the title of Most Ostentatious already.

The $40 million Trump National is festooned with reminders of The Donald’s love of excess. Everything on the course – including the bottled water in the golf carts bearing the owner’s name – screams Trump.

“One half-expects to see a bank of slot machines emerge at any moment,” one reporter wrote recently.

The most spectacular feature is the massive waterfall behind the 13th green, which stands 100 feet high and 150 feet wide.

It’s a mini-Niagara Falls that Trump and golf course designer Jim Fazio created by knocking down half a mountain and pumping 5,000 gallons of water per minute to the top.

“You’ve never seen anything like this,” Trump exclaimed during an early morning tour he gave to The Post. “It’s the most expensive golf hole ever built!”

While that claim could not be verified, it certainly looks expensive.

“The only thing he didn’t do is carve his face in the rock like Mount Rushmore,” quipped one wag.

Trump claimed the 13th hole alone cost between $6 million and $7 million – more than some entire courses.

“It took five years in the planning process and two years to build, and it’s definitely been a labor of love,” said Trump.

Unfortunately, Trump’s love was not requited by the 13th hole – which he bogeyed during an inaugural round of tournament golf last Saturday.

“I hate that hole,” he declared. “That hole has just killed me since the day I built it. I think I’m going to disassemble it.”

Despite his disappointment, Trump had a pretty good day.

He was bubbling with the excitement of a new dad. At a reception after the round, he cracked jokes like a Catskills comedian, a few of them rather blue.

When he introduced the members of the town’s local planning board – some of whom voted against the course – he quipped, only half jokingly: “These guys bust my ass for five years, and now I’ve got to introduce them?”

Trump played his round with old pal Ron Howard.

“He’s really competitive,” Howard said, after the round in which The Donald’s team lost a best-ball competition to a group of wealthy doctors. “You don’t want to miss any putts when you’re on his team.”

Trump won a “closest to the pin” competition on the par three 15th hole, hitting his tee shot 6 feet from the cup.

“The prize for the closest to the pin competition is a trip for two around the world – preferably with a supermodel,” a facetious Trump said to laughs. “And the winner is – Donald Trump!”

Then he added: “Let’s see what I really win. A pair of shoes, big [bleeping] deal.”