MGM GRAND GARDEN Arena was packed with great fighters that night. It was Sept. 27, 2014, and the headline bout of UFC 178 had a championship at stake. The Las Vegas spotlight was also shining on the return of a long-gone former champ. There were even three future titleholders sprinkled throughout the undercard. One of them would soon take over mixed martial arts.

Conor McGregor was stepping into the Octagon for only the fourth time. He had won his first three UFC outings, and he had done so with gusto, intoxicating an expanding fan base with brazenness in his fights and at the microphone. He was a disruptor on the rise, but on this night, he faced a sizable step up the ladder. His opponent was a fellow young climber named Dustin Poirier, who was more seasoned with 10 trips inside the UFC cage.

Even at that early stage of his MMA rise, McGregor had established himself as a polarizing figure. His thunderous fists inside the Octagon were widely acclaimed, but his hard-hitting mouthiness was drawing a mixture of bouquets and backlash. There were those who envisioned McGregor's well-timed precision with strikes and callouts as a rocket ship to the top of the sport, and there were those who grumpily discredited him as no more than a hyped-up, promotional darling who would crumble like a house of Joker cards once the matchmaking got tougher.

McGregor had something to prove that night in Las Vegas, and it came forcefully and surgically in the beating he put on Poirier. By barely breaking a sweat in a first-round knockout, McGregor coaxed all but the most stubborn skeptics onto his full-steam-ahead, hype express. The victory over Poirier was rocket fuel.

Six and a half game-changing years later, the pair will renew their acquaintance on Saturday in the main event of UFC 257 in Abu Dhabi, United Arab Emirates. While the circumstances surrounding the two fights might appear totally different, at their core they are fundamentally the same.

Once again, McGregor faces a career-pivoting test. This is his first fight in over a year, and his most important since an unsuccessful challenge against lightweight champion Khabib Nurmagomedov in 2018. A victory would legitimize the 32-year-old Irishman's claim to another shot at the title belt he once owned. A defeat would send McGregor tumbling from the top tier of fighters in MMA, a sport that revolves around him in both storyline and bottom line. He would be relegated to a spectacle -- a main event spectacle, to be sure, because his name will still sell fights.

But would it be enough for this proud fighter to see his name at the top of the marquee even as a noncontender?

MCGREGOR HAS HAD a grander impact on the sports world than any MMA fighter in history. He cannot be defined by just bluster and oversized hype. McGregor has authored some breathtaking performances, most notably a 13-second knockout of longtime featherweight king Jose Aldo in 2015. That was Step 1 in McGregor's march toward becoming the first to reign as champion in two UFC weight classes simultaneously. It was an accomplishment that will always shimmer on his résumé.

As was the case at the time of the first Poirier fight, though, McGregor is now the focal point of a split in perceived reality. One way to view the McGregor of 2021 is as a transcendent star who has spent the past several years becoming MMA's richest athlete by expanding his brand beyond the cage. He has done that by taking on an unthinkably lucrative boxing match with Floyd Mayweather and by launching a hugely popular global whiskey brand. The other perspective on today's McGregor is that, with only one victory in the past four years and just two dates inside the cage to his name, he is more celebrity than fighter. An athlete who lost focus, strayed and only now is getting serious again, perhaps too late.

The luster of McGregor's success in the Octagon has been tarnished by troubles outside of it. He has been arrested multiple times for transgressions caught on video -- attacking a bus full of UFC fighters, punching a Dublin pub patron and destroying the phone of a fan trying to snap a picture. His rants during the buildup to the Mayweather and Nurmagomedov fights devolved into racism and xenophobia. There also were reports of sexual assault investigations in Ireland and France. McGregor's name has been in the media for all the wrong reasons.

If McGregor can score an impressive win over Poirier, who is ranked No. 2 in a lightweight division in which No. 1 Nurmagomedov has announced his retirement, that would instantly erase questions about McGregor as a fighter that have arisen during his largely inactive recent years.

If McGregor loses? His status as a UFC cash cow is not in jeopardy -- he'll remain a box office draw no matter what happens this weekend -- but a defeat would deliver a serious blow to his relevance among 155-pound contenders and could throw a bucket of cold water on his competitive fire.

Remember that fire? The last time we saw it truly ablaze in the UFC, it was consuming Madison Square Garden in New York on Nov. 12, 2016. That was the night McGregor became the promotion's first champ-champ by knocking out Eddie Alvarez to add the lightweight belt to the featherweight strap he already owned. McGregor came into that fight already a star, but his performance at The World's Most Famous Arena set him apart. As he celebrated atop the cage with UFC belts slung over each shoulder, a sight never before seen, McGregor was sitting on top of the world.

Then, the world stopped and spun the other way. Never again would we see those two hunks of shiny brass and leather in McGregor's possession. He did not defend either belt, and by the spring of 2018, he was stripped of both for inactivity. By then, he had also detoured to a boxing sideshow and, predictably, been knocked out by Mayweather.

His glorious swagger knocked off-kilter, McGregor returned to the Octagon in October 2018 and became just another victim of a Nurmagomedov mauling. McGregor did not have it in him to engage the champ in a back-and-forth blockbuster, as many expected to see. McGregor had always seemed a step above the rest, capable of more because he expected more from himself and for himself. But has the McGregor magic been spread so thin in recent years that it has disappeared like a rabbit in a top hat?

SATURDAY NIGHT'S REDO with Poirier is a formidable challenge, much more so than McGregor's dance last January with a faded Donald Cerrone, whom he demolished in 40 seconds. McGregor made quick work of Poirier, too, when they met in 2014, but the 2021 version of the Louisiana lightweight is more mature, resilient and dangerous.

It's admirable that McGregor is even taking this fight. His star power alone could have qualified him -- in the eyes of UFC matchmakers and bean-counters, at least -- for a title challenge. McGregor, like he did so often during his rise in the sport, is taking a risk to earn his chance to grab for the old golden ring.

This weekend will test McGregor's readiness and put his standing in the sport in peril. Getting beat up by the indomitable Nurmagomedov is one thing, but dropping a fight against Poirier -- an excellent fighter, to be sure, but one lacking the aura of the champ -- would bury McGregor in the hierarchy of title contenders. Would McGregor have the resolve to build himself back up? Would he have that fire? Or would he be preyed upon by lightweights suddenly emboldened by spotting a previously undetected vulnerability?

McGregor is a master of mind games. That has always been his superpower. His self-belief is off the charts, and his flair for browbeating his opponents has worked like a crisp jab to fill their heads with rage and undermine any strategy they brought into the cage. McGregor can counteract out-of-control aggression. But if Poirier maintains his poise and cuts through the gamesmanship, why can't the next guy? If McGregor can no longer intimidate, can he still shine at the highest level?

McGregor's appeal is not wholly dependent on him being untouchable in the cage. It helps, of course, because in all sports, there's an aura around athletes who are unstoppable. But so much of what makes a McGregor fight special is contained in the pomp and circumstance, the weeks of anticipation building to the spectacle of him entering the bright stage on fight night. Even if McGregor gets evicted from Contenderville on Saturday night, he'll continue to reside in a majestic mansion on Money Fight Avenue. His swagger will always sell.

Still, what has made McGregor fights so grand is that they've meant something more enriching than dollars and cents. The two championship fights he won, and even the one he lost, all produced as much heat as the spotlights shining down on them. Those and pretty much all of his other fight nights have been memorable in the biggest way possible -- from the mastery and artistry of the fighter to the decibels and joyousness of the crowd. There is no other fighter in combat sports whose presence lifts an arena off the ground and into the stratosphere. That happens only when the gold is within McGregor's reach.

On Saturday night, we find out if the MMA world will still orbit around that Conor McGregor.