The 300th numbered card in the 15-year history of Bellator MMA takes place on Saturday in San Diego with three title bouts atop the marquee. 

An injury to Linton Vassell pulled his rematch with heavyweight champion Ryan Bader from the main event inside Pechanga Arena. Instead, lightweight champion Usman Nurmagomedov will look to make his second title defense in the new headlining bout when he faces former champion Brent Primus in a semifinal matchup of the Bellator Lightweight World Grand Prix.

As we draw closer to this weekend's historic event, let's take a closer look at the biggest storyline entering Bellator 300. 

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1. Nurmagomedov might be the best fighter on Bellator's roster

And that's saying a lot given how deep, particularly from the standpoint of homegrown talent, that Bellator currently is. At 25, the 17-0 cousin of former UFC lightweight king Khabib Nurmagomedov, looks to continue upon the red-hot start to open his career as the native of Russia welcomes his third straight former lightweight champion. Although Brent Primus is 38 and just 2-2 over the last two years, he appears to be rejuvenated of late and could prove to be the toughest pro challenge to date for Nurmagomedov on paper. The winner takes one step closer to the $1 million tournament prize and the last-minute headliner change ahead of such a historic event allows Bellator to showcase even more aggressively how dynamic of a well-rounded talent that Nurmagomedov is. Yes, Nurmagomedov can wrestle, like his namesake, and he's a constant submission threat. But he's also a dynamic striker who trains alongside the other top lightweight in the world, UFC champion Islam Makhachev. 

2. The loss of AJ McKee has hurt the Lightweight Grand Prix's allure

McKee, the 28-year-old phenom and former featherweight champion, pulled out of a July quarterfinal bout due to medical issues that removed him from the 155-pound tournament before he could even debut. The biggest problem is that it robs fans of the best matchup Bellator could make on paper, and the one expected for the championship final, pairing McKee and Nurmagomedov. Former champion Patricky Pitbull stopped replacement Roberto de Souza, which sets up an upcoming semifinal bout against Nurmagomedov's red-hot countryman Alexandr Shabily. Although there is still heavy intrigue in watching a future star like Nurmagomedov navigate a difficult bracket while being forced to defend his Bellator title each time out, there was no greater test of the Dagestani's pound-for-pound pedigree than that of McKee. 

3. Cyborg-Zingano was the one that got away

Over a pioneering 18-year pro career, Cris Cyborg has only suffered two defeats -- a submission loss in her 2005 debut and a first-round knockout loss to Amanda Nunes in their 2018 UFC title bout. The Nunes loss was never avenged because Cyborg had such an impactful falling out with the promotion in the aftermath that it sped up her exit to Bellator, where the reigning women's featherweight champion is 5-0 with four stoppages. The 38-year-old Cyborg will look to clean out one of the last remaining names from her era that she has yet to face off against when she welcomes former UFC bantamweight title challenger Cat Zingano. Although the 41-year-old Zingano has won all four of her Bellator fights since debuting in 2020, she had previously lost four of her final UFC fights leading up to it. The fight against Cyborg has become personal for Zingano, who has accused the Bellator champion of bullying her verbally for years. The bout was further delayed by Cyborg's lengthy free agency period, which ended with her re-signing with Bellator CEO Scott Coker to a "historic" multi-year deal (although terms were undisclosed). Cyborg is the only fighter in MMA history to have won world titles in Bellator, UFC, Strikeforce and Invicta. She was also unbeaten for nearly 13 years until the Nunes loss.

4. Bader-Vassell II would've likely looked different than their first meeting

Before both would make dramatic reinventions for themselves at heavyweight, Bader once defeated Vassell via second-round TKO in defense of the light heavyweight title he held for three years beginning in 2017. But six years later, this matchup was heading toward a rematch fought on much different terms until Vassell pulled out just days before with an illness. The 40-year-old Vassell has completely rebuilt himself as a heavyweight, relying on wrestling and the increased power due to his increase of muscle. Vassell has won five straight at heavayweight since losing his debut to Valentin Moldavsky in 2019, with four wins coming by knockout. Although Bader, 40, has lost his last two fights at 205 pounds, he remains unbeaten as a heavyweight. Hopefully, the promotion will be able to reschedule soon. 

5. It's champion vs. former champion at women's flyweight 

Although Liz Carmouche's title winning victory over Juliana Velasquez in 2022 felt dubious only because it came via questionable stoppage, she converted all of her doubters into believers by the ease in which she submitted Velasquez in the rematch. Two fights later, the 39-year-old Carmouche welcomes the division's most decorated former champion in Ilimi-Lei MacFarlane. Although she hit a recent two-fight losing skid, which included her losing her the belt to Velasquez, the inaugural 125-pound champion has won two straight and holds the division record with four title defenses. The fight against Carmouche is interesting not just because the two are close friends and longtime training partners but because the two publicly campaigned for this fight to take place. MacFarlane has also teased this could be her retirement bout, which adds extra layers to the storyline.