One defeat cannot wipe out all those trophies, all that progress, all those winners under snowballing pressure. But a loss to Rafael Nadal in the United States Open final would have a big impact on the balance of power and the bottom line in the record books.

If the No. 1-seeded Djokovic can maintain his newfound mastery over the No. 2 Nadal, he will hold three of the four Grand Slam singles titles after winning the Australian Open and Wimbledon and stand alone atop the men’s game, which has rarely been so tough to climb.

But if Nadal, the French Open champion, can find, in his own word, “solutions” and stop his five-match losing streak against Djokovic, he and Djokovic will each have two major titles this year with potential duels to come at the ATP World Tour Finals in London and in the Davis Cup final.

And just what might be these solutions? “I think I going to do serve and volley,” joked Nadal as laughter reverberated through the news-conference room at Flushing Meadows.

It was quite a change in mood in the same place where, earlier in the tournament, Nadal had slumped in his chair and ended up on the floor because of leg cramps. Nadal, a resilient sort on court and off, eventually returned to his feet and resumed answering questions, and he is now — after a frustrating summer — just one victory from defending his United States Open title.

There were some deeply encouraging signs against Andy Murray in the semifinals. Nadal slashed his forehand with great strength and conviction, particularly down the line, and he generated pace with his first serve that was reminiscent of his breakthrough run to the title in New York last year.

But Murray, still overly prone to dark thoughts, was hardly the same steady flame that Djokovic has been this season. Though Murray produced plenty of quality, even spectacular, shots, he also missed too many routine ones and failed to take consistent advantage of Nadal’s two-handed backhand landing short in the court.

If that continues, Djokovic will presumably be more opportunistic. And despite the grand expectations he has generated for himself with his astounding 63-2 record in 2011, Djokovic may also feel more liberated than usual after again staring down elimination against Roger Federer in the semifinals.

A year ago on the same court and in the same round, Djokovic saved two match points on his serve and went on to beat Federer in five sets. This time, he increased the degree of difficulty by rallying from a two-set deficit and saving two match points on Federer’s serve before going on to win in five.

“I would lie if I say, I didn’t think I’m going to lose,” Djokovic said of the match.

No man has won the United States Open after saving a match point since Andy Roddick in 2003, but it is difficult to see how a victory like Saturday’s won’t bolster Djokovic’s sense of destiny.

“It’s all mental in the end,” Djokovic said. “It’s all mental to be able to handle the pressure well, to be able to step in and take the chances that are presented.”

Such self-belief has, until this season, been Nadal’s trademark, but five losses in five finals against Djokovic has put a dent in Nadal’s armor as well as in his career edge over Djokovic, which has shrunk to 16-12. Nadal’s performance in the Wimbledon final was particularly telling. He was visibly frustrated, visibly pressing, visibly confused.

“Probably played my worst match against him,” said Nadal, who was quick to clarify that this was no coincidence.

“I am not very happy about my mental performance against him this year. Because for moments I didn’t really believe 100 percent with the victory. That’s a big problem.”

In a sport in which facades are standard equipment, Nadal has been unusually frank about his Djokovic complex. And though he said he intended to do all in his power to rectify the big problem Monday, he also, unusually, hedged his bets.

“If I’m not ready to change for Monday,” he said, “I have a goal to do it for next year.”

If Nadal, who has 10 Grand Slam titles to Djokovic’s 3, is going to shift the momentum in 2011, he will have to serve particularly well. He will want to put a high percentage of first serves into play with an emphasis on those to Djokovic’s body and on the sliced serve wide in the ad court that Nadal used to fine effect against Murray.

Nadal, whose touch remains underrated, will need to hit his backhand slice crisply and rush the net occasionally to keep Djokovic from locking into the baseline rhythm that allowed him to get the better of Nadal in their previous matches this year. Nadal will also need to hit his trademark forehand with the consistent ferocity that was lacking at Wimbledon but which was on full display last year, when he beat Djokovic in four sets in the United States Open final.

“I saw that match a lot of times,” Nadal said. “I know what I have to do, but I don’t know if I’m going to be able to do it.”

Relying on baseline winners against the supremely mobile, beautifully balanced Djokovic has been a fool’s errand this season, but Federer, his signature forehand back to writing with verve, managed the risk-reward ratio successfully for long stretches of Saturday’s match before cracking for good with a big assist from Djokovic’s full-blast forehand return winner on Federer’s first match point.

It was both the shot of a desperate man and the shot of a champion, and it was a reminder to Nadal — surely unnecessary at this stage — that this year’s Djokovic cannot be counted out until the handshake or perhaps even the on-court interview.

Taking him out will require quite an effort and — still strange to say — quite an upset. But if Nadal, that rare defending champion who qualifies as an underdog, can somehow lift himself up and pull it off, the 2011 season will suddenly look very different.