Cain Velasquez's comeback from a 31-month layoff was over shortly after it began.

The two-time former champion and arguably the greatest heavyweight in UFC history walked into a pair of right hands before his left knee gave out, leading to a shocking 26-second loss to former title challenger Francis Ngannou on Sunday in the main event of UFC Fight Night in Phoenix, Arizona.

The loss, which headlined the first UFC card on ESPN, was reminiscent of Velasquez's 64-second loss to Junior dos Santos in 2011 when Velasquez, fighting through a knee injury, lost his title in the first show of UFC's then-landmark deal with Fox. Sadly, Velasquez did nothing but add to his recent legacy of being injury prone with how he lost on Sunday.

The 36-year-old Velasquez (14-3), who has fought just twice in the last four years, was also given no favors by coming back against the one-dimensional, yet destructively dangerous Ngannou (13-3). Velasquez shot in for an early takedown attempt and was caught with a short right cross and an uppercut.

Just as Velasquez attempted to steady himself to avoid going down, his left knee gave out. Ngannou instantly leaped onto the fallen Velasquez to land a pair of hammer punches just as referee Jason Herzog dove in to wave off the fight.

"Give it up to Francis. He came in here and did his job," Velasquez said. "I stayed a little too close, too early.

"[My knee] just kind of buckled there on the shots. I stayed a little too close and it was dangerous. What are you going to do?"

A native of Yuma, Arizona, Velasquez returned to a hero's welcome in Phoenix. The former Arizona State wrestling standout took extra time ahead of his most recent return -- not only to make sure he was physically healthy, but to strengthen himself mentally after taking an extended leave from training to enjoy the birth of his son, Cain Jr., in 2018.

Now it's back to the drawing board for Velasquez, who hadn't fought since he ended a 13-month layoff in 2016 by obliterating Travis Browne in one round at UFC 200.

"[I'll return] as soon as I'm all good," Velasquez said. "I felt super ready for this fight; even came in here super calm and relaxed and ready to go. This is why this sport is so great, you never know what will happen at any time. I can give you guys more and you know I can give you guys more. I'm truly sorry for this."

While the latest chapter of Velasquez's rollercoaster journey undoubtedly stole the headlines, the victory was a massive one for Ngannou, the 32-year-old native of Cameroon who was exposed in his January 2018 loss to then-champion Stipe Miocic as a one-trick pony.

"I promise you guys, I'm back," Ngannou said. "As I've said before, I'm back and you are going to see me around again. I told you yesterday I had some surprise for you and I hope you like it."

Despite a subsequent loss to Derrick Lewis last July that saw even UFC president Dana White publicly question Ngannou's attitude and commitment to the sport, "The Predator" bounced back in a big way by knocking out Curtis Blaydes in their November rematch.

With such a demonstrative victory over a fighter the caliber of Velasquez, there's little question that Ngannou has catapulted his name back into a title picture which includes current champion Daniel Cormier, Miocic and the possible additions of Brock Lesnar and Jon Jones.

"[The finish] was very fast so I didn't even realize what happened," Ngannou said. "It was very fast. I felt good and I'm just here to have fun and relax and enjoy my fight.

"I've been waiting for this fight since two years ago because I know I needed a challenge of the likes of Cain to prove myself."

CBS Sports was with you for every punch, kick and submission attempt from Phoenix with our live blog below. If you are having trouble viewing the blog, please click here.

UFC on ESPN 1 results

Francis Ngannou def. Cain Velasquez via first-round KO (punch)
Paul Felder def. James Vick via unanimous decision (30-27, 30-27, 29-28)
Cynthia Calvillo def. Cortney Casey via unanimous decision (29-28, 29-28, 30-27)
Kron Gracie def. Alex Caceres via first-round submission (rear-naked choke)
Vincente Luque def. Bryan Barberena via third-round TKO (strikes)
Andre Fili def. Myles Jury via unanimous decision (29-28, 29-28, 29-28)
Aljamain Sterling def. Jimmie Rivera via unanimous decision (30-27, 30-27, 30-27)

UFC on ESPN 1 commentary, updates

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