As she prepares to fight Cris "Cyborg" Justino for the women's featherweight title Saturday at T-Mobile Arena in Las Vegas, Holm has a chance to shock the world again.
This will be the second time she's climbed into the Octagon with one of MMA's unbeatable champions—and we all remember what happened the first time.
Holm's astonishing head-kick knockout of Ronda Rousey at UFC 193 in November 2015 caused a tectonic shift in the landscape of the sport. It ended Rousey's reign as both bantamweight champ and the UFC's biggest draw while simultaneously teeing Holm up to be the fight company's next female superstar.
That star turn never fully materialized, as Holm went on to drop her next three fights in a row.
If the Rousey victory was one of MMA's biggest surprises, Holm's consecutive losses to Miesha Tate, Valentina Shevchenko and Germaine de Randamie turned it into one of the sport's greatest missed opportunities.
Those defeats fashioned Holm into an odd figure in combat sports.
Her previous professional boxing experience and hot start on the independent MMA scene made her the hottest of hot prospects. The victory over Rousey had her poised to cash in on that considerable potential. Then she squandered it, effectively dropping out of the conversation as current bantamweight champion Amanda Nunes took over the division.
Now against Justino, Holm will get something approaching a do-over.
In one fell swoop, she might change much of what we think of her, becoming a two-time, two-division UFC champion and rebooting herself at 145 pounds. She's going off as nearly a 3-1 underdog to Cyborg, according to OddsShark, but represents perhaps the most interesting stylistic challenge of the ferocious titlist's career.
Holm excels when her opponents bring the fight to her, and Cyborg is nothing if not dependably aggressive. Justino won't be as reckless as Rousey was, and she'll be even more dangerous, but fans are already used to seeing Holm do the impossible.
"I think there are similarities with the feeling of it," Holm said during last week's UFC 219 media call. "Just knowing that people are having a little bit of doubt. To be the underdog [again] and come in—I think people think, 'Oh, OK, well Holly is capable of doing some [surprising] things.'"
Certainly, Justino appears as invincible now as Rousey did then. Cyborg may have a far less cozy partnership with the UFC than the one Rousey enjoyed, but the results have been just as dominant.
Unbeaten since 2005, Justino has amassed a record of 18-1-1, including 12 straight knockouts. Along the way she's established a reputation as one of the most fearsome fighters in MMA history.
Her only recent career hiccups include a positive steroid test in 2011 that turned a successful Strikeforce title defense into a no-contest and an icy relationship with the UFC, which has kept her from taking her rightful place among the organization's biggest drawing cards.
Like Holm's letting the wave of notoriety she got by beating Rousey stale into disappointment, Cyborg has also spent much of her career in the Octagon watching the biggest opportunities float slowly by.
For years, fans hungered for a Justino vs. Rousey superfight, but Cyborg's inability to make the 135-pound limit—and perhaps Rousey's unwillingness to take the fight in the first place—made it impossible. After years of public spats and dead-end negotiations, Cyborg didn't even arrive in the UFC until May 2016, six months after Holm laid Rousey flat.
Even after officially becoming a UFC performer, Justino's path has been rocky.
Early on, matchmakers didn't seem to know what to do with her, booking her in a series of 140-pound catchweight attractions. When the company finally moved to create a featherweight division, another negotiating stalemate kept Justino out of the inaugural title bout. Instead, De Randamie defeated Holm at UFC 208 to become the first 145-pound women's champ in promotional history.
Still, Cyborg's shadow loomed large. De Randamie spent just 128 disastrous days with the title before the UFC stripped her, citing her refusal to defend against Justino.
Cyborg defeated Invicta FC bantamweight champ Tonya Evinger via third-round TKO to claim the vacant title in July 2017. Afterward, the fight company hit the reset button, booking the fight it wanted from the beginning: Cyborg vs. Holm.
Holm made the bout possible by following up her loss to De Randamie by heading back to bantamweight and scoring a rehabilitative knockout over Bethe Correia in June 2017. Given the shallow nature of the new featherweight class—where the UFC doesn't even offer rankings on its official website—that was good enough to make her attractive as Cyborg's next opponent.
For her part, Justino says she has known this fight was coming since the night she watched Holm KO Rousey.
"I watched the fight," Cyborg said during the UFC 219 media call. "On that day, I was making plans to fight Ronda, but when Holly beat Ronda, I said one day soon, I'm going to fight Holly."
It will be a massive opportunity for both fighters, especially Holm.
For the Albuquerque, New Mexico, native, it's a chance to beat yet another MMA icon and to pair her improbable victory over Rousey with one perhaps even more unexpected.
Despite the fact Holm's own UFC career hasn't quite lived up to expectations, defeating both Justino and Rousey would seal a unique, if admittedly strange, legacy.
Becoming featherweight champion would have obvious privileges. For Holm, it could be the difference between being remembered as an also-ran and retiring among the all-time greats.
The fledgling 145-pound title offers new life to the handful of contenders ready to step in from bantamweight. If Holm can become champion there, it could set up a series of interesting and promotable matchups for her against contenders such as Cat Zingano, Megan Anderson or Nunes.
Maybe Holm could even close out her career in a style befitting the hype fostered by her win over Rousey.
Instead of being remembered as a one-hit wonder, she might go down as MMA's giant killer.