Rafael Nadal is back in the quarterfinals of a Grand Slam event for the first time since 2015, when Novak Djokovic insolently dismissed him from the French Open, the tournament Nadal once dominated.

That loss was a painful humiliation for Nadal, part of a downward spiral that was accelerated over the ensuing months by self-doubts that had a corrosive effect on his effectiveness. Injury, which first became a steady companion for Nadal way back in 2009, also played a large role in a swoon that saw Nadal start this year ranked No. 9, a 14-time Grand Slam singles champ written off by many as a shadow of his former "King of Clay" self.

But hold everything. Should Nadal survive the bombardment in store when he plays ace machine Milos Raonic in Wednesday's quarterfinals, he has an excellent chance to make the final. In a tournament that lost its top two seeds, Andy Murray and Novak Djokovic, respectively, Nadal could potentially play a title match against his old frenemy, Roger Federer.

Looking ahead to his match with Raonic, Nadal told the press: "I need to be very focused with my serve and play aggressive. If I am not playing aggressive, then I am dead, because he plays aggressive."

Nadal sounded like he couldn't remind himself enough of how confidently he must play, and it's understandable. About two years ago, his signature self-assurance and steady nerves deserted him. As Pat Cash, a former Wimbledon champ, said in an interview with the UAE's Sport 360 website in late 2016: "For Rafa, it's about rebuilding his confidence. Last year, we saw him just losing his confidence under pressure. When he's in good form, his depth [of shot] is unbelievably good, and when he's not in good form, it's really poor, and the guys are taking advantage of that now."

Nadal's crisis has been conspicuous. He built a glorious career on his stamina and unrelenting effort that so often left him the last man standing. But Nadal lost three consecutive five-set matches before he finally won one again in the third round of this Australian Open.

All along, Nadal has been humble about his prospects and scrupulously honest about his problems, including those quaking nerves. That has hurt his image. The swashbuckling youth in those sleeveless T-shirts, with his long chestnut locks girded by a headband worthy of a samurai, seemed to have morphed into a 30-year-old bundle of nerves with a bald spot on top of his head and a sad tale to tell. The respect Nadal once inspired was increasingly flushed with pathos.

But imagine for a moment that Nadal wins this tournament or, now that he has returned to a semblance of his former self, continues to build on his recent success?

Nadal is just three Grand Slam titles behind Federer's record of 17, and he is two ahead of Djokovic. Nadal has already won the French Open a whopping nine times. Another win in Paris is not just possible; by late May, it might seem likely.

"At some stage, it seemed that I could beat some records," Nadal told Eurosport in an interview early this year. "People changed their opinion, but you never know what can happen. It depends on injuries and other things. Every year, some things can happen, and I will try to be ready."

People changed their opinion.

In Nadal's case, they might have written him off prematurely. Without the bombast and presidential bearing of Djokovic or the slick self-regard of Federer, Nadal made it easy to take him for granted. Yet if the history of the Big Four were written with the evidence at hand, Nadal -- not Federer nor Djokovic -- would be the pivotal figure.

That isn't just because his stats bear comparison with those of Federer. It is because Nadal has been responsible for so much of what has happened at the top of the game from the very moment he emerged on the scene, as the first -- and for a long time lone -- viable challenger to Federer.

To borrow a phrase once used by New York Yankees slugger Reggie Jackson to describe his outsize role with his team, Nadal is "the straw that stirs the drink."

Nadal matured at a time when Federer ruled the game. Over time, he did what very few predicted. He hunted down the Swiss star on Wimbledon grass to usurp the top ranking and ultimately came to dominate their personal rivalry 23-11. Nadal's successful "Stop Federer" campaign inspired those who followed, including a brace of players barely a year younger than Nadal, Djokovic and Murray. Those two understood that if clay-court expert Nadal could master Federer on grass and hard courts, anything was possible.

Over time, Djokovic has crept ahead of Nadal in their rivalry 26-23. That tally includes seven consecutive wins in their most recent matches (in which Djokovic has been at his peak and Nadal struggling). Nadal holds a 17-7 edge on Murray, who has been perhaps the greatest beneficiary of Nadal's absence. But by and large, Nadal's influence is a tale the numbers don't tell.

Milos Raonic is one of the Next Four, along with Nick Kyrgios, Dominic Thiem and Alexander Zverev. Mark Kolbe/Getty Images

Although Djokovic first maximized his talents in 2011, his most productive period coincides with Nadal's decline and lengthy absences. Similarly, Nadal was an enormous obstacle that Murray was able to surmount only periodically. Murray has had back-to-back wins over Nadal just twice in their 24-match history, and Murray never had to play Nadal during his great run in the second half of last year.

We don't know what would have happened had Nadal remained healthy -- or never lost confidence. But it seems clear that removing Nadal from the mix was a little like taking a critical card out of a house of cards. Similarly, it's impossible to predict what a Nadal resurgence might mean to the future of the Big Four -- or to Stan Wawrinka, who has just three wins in 18 matches with Nadal.

These issues and statistics are going to take on greater urgency and significance if Nadal can sustain his momentum. He's healthy, and the way the game has gone, his age of 30 ought not to be an impediment. Nadal hasn't always helped his own cause with his humility, though that quality earned him the enduring admiration of legions of fans.

Asked by Eurosport to name the greatest male player of all time, he said, "I would say it is between Federer and Laver. I think it's a correct definition thinking about the tennis history. Then we will see. There are some good players that are still playing, like me. Djokovic is one of the best players as well. He is still playing and could be the best player ever."

The "like me" was pretty deeply buried in his quote and easily missed. Nadal certainly didn't seem to want to dwell on it. Who could blame him, given what he has been going through for almost two years? First things first, he appears to be thinking.

Nadal popped one of his trademark rhetorical questions for the press after his recent five-set win over Alexander Zverev: "For the confidence, for lot of things, are very important to win these kind of matches, no? I worked a lot during all December to have the chances to compete well [in] these kind of moments."

Raonic had only one win over Nadal in seven previous matches before he added another in Brisbane a few weeks ago. The 26-year-old Canadian is recovering from a flu, but it seems to have had minimal impact on his performances in Melbourne.

Nadal is recovering from a more nagging condition, a largely mental one that has been easy to diagnose but hard to cure. He knows Raonic will put him under enormous pressure to hold serve and make passing shots. Looking ahead, Nadal said of Raonic, "His serve is huge, and he's playing very aggressive from the baseline."

Nadal knows what's coming, adding, "I hope to be ready for it."