Rafael Nadal will face Novak Djokovic in the U.S. Open men’s singles final on Monday. (EMMANUEL DUNAND/AFP/Getty Images)

Monday’s U.S. Open men’s final marks a resumption of the most heated rivalry in tennis, pitting world No. 1 Novak Djokovic against No. 2 Rafael Nadal.

Nadal, the 27-year-old Spaniard with the spin-slathered strokes and fierce fighting spirit, boasts a 21-15 record against Djokovic, a 26-year-old Serb with unparalleled retrieval skills and a drive equal to Nadal’s.

But asked how he feels about taking on Djokovic for a 37th time — and the third time in four years with the U.S. Open title at stake — Nadal smiled after mulling the prospect.

“I prefer to play against another one,” he said. “We have to be honest, no? We don’t have to be stupid.”

It was an acknowledgement of respect on Nadal’s part — an admission that whether he wins or loses, Djokovic will extract every ounce of energy, every drop of effort in pursuit of the title.

The regard is mutual.

They have split their previous U.S. Open finals, with Nadal winning in 2010 and Djokovic in 2011.

This season, each has added one Grand Slam title to his portfolio. Djokovic won the Australian Open; Nadal claimed a record eighth French Open in June.

Djokovic will retain his No. 1 ranking regardless of Monday’s outcome. But Nadal would stake a compelling claim with a victory, becoming the only man to win more than one major this season.

It would be a remarkable achievement given the tendinitis Nadal has battled in recent years — a consequence of his punishing style of play, the pounding it takes on his joints and his compulsion to practice with the same fury with which he competes.

Nadal was sidelined seven months to recover from his latest bout, which flared up during his short-lived run at Wimbledon in 2012. He missed the London Olympics, last year’s U.S. Open and the first major of this season, the Australian Open.

But since returning to competition in February, Nadal has compiled the most daunting record in the men’s game. Heading into the U.S. Open, he had reached the final of 11 of the 12 tournaments he entered and won the title nine times.

His six victories here brought his 2013 record to 59-3, which includes a 21-0 mark on hard courts. He has not lost a match since his shocking first-round defeat at Wimbledon in June.

Said Djokovic: “With no doubt, he’s the best player in the moment this year, no question about it.”

Nadal should also be the fresher man Monday, having breezed through his straight-sets semifinal victory over Richard Gasquet in 2 hours 21 minutes. Djokovic labored 4 hours 9 minutes in a five-set slugfest against Stanislas Wawrinka, playing the match of his life.

It’s good news for Djokovic, then, that U.S. Open officials this year abandoned their long-criticized practice of staging the men’s final the day after the semifinals. For the first time since 1954, the men have a scheduled day off before contesting the final.

Nadal stopped short of saying that the change guaranteed a higher quality final, but conceded it would make it more fair.

With both fully fit and rested, Monday’s final has the makings of a tremendous match.

Apart from 32-year-old Roger Federer, whose decline was painfully evident in his fourth-round defeat here to a player Nadal crushed 6-0, 6-2, 6-2 two days later, no active men’s player boasts more major titles than Nadal (12) and Djokovic (six).

But what truly sets them apart is a refusal to view themselves as finished products. Both have thrown themselves into shoring up their weaknesses these last years. Djokovic, by honing his volley and serve; Nadal, by flattening his strokes, stepping in closer during rallies and attacking more — all of which have made him more potent on hard courts.

“Guys like Nadal and Djokovic are making their opponents run a lot more than they’re running,” says four-time U.S. Open champion John McEnroe, who has followed both careers as an analyst for multiple networks. “They have figured out how to improve themselves moving forward, which is very impressive.”

Then there is the uncommon mental toughness they share.

In Nadal’s case, it stems from a passion for tennis as innate as breathing and his drive to become as close to a perfect player as possible, intolerant of shortcomings in his strokes and heart.

Djokovic attributes his to his war-torn childhood in Belgrade, Serbia, where he and his friends played tennis all day when the incessant bombings canceled school.

“After a week or two of the bombings, we just kind of moved on with our lives,” Djokovic recalled. “We just let the life decide for us; it was not in our control.”

The experience, he said, left Serbs of his generation more appreciative of life, more determined to live each moment fully.