One of the most chaotic lead-ups to a UFC pay-per-view card culminated with the three top-billed fights all swapping opponents, with Nate Diaz now facing Tony Ferguson in the main event of UFC 279 on Saturday night.

UFC president Dana White already had called it an unprecedented situation when he was forced to cancel the traditional fighters' press conference on Thursday due to an uncontrollable brawl backstage between multiple fighters and their entourages, before further shenanigans took place at the weigh-ins.

Needing to weigh within one pound of the 170lbs welterweight limit, Khamzat Chimaev – in his first main event – came in at a staggering 178.5lbs, missing weight by seven-and-a-half pounds. 

While fighters are given an extra hour to try and shed the extra weight – usually one or two pounds at the most – Chimaev was so far away that there was no point, all but cancelling his fight against Diaz as he refused to concede the massive advantage to his already favoured opponent.

While a few pounds may not seem like it would decide an outcome, competitors who have missed weight have been known to thrive on fight night due to the fact they did not have to drain themselves all the way down to the required number. 

It raises questions about the validity of cutting weight at all, with other promotions such as top Asian brand ONE Championship outright banning the practice by forcing fighters to pass hydration tests in the lead up to the fight to ensure they are not dangerously dehydrated in the effort to shed the last few pounds.

With the main event off, the call was made to Ferguson to step in on short notice, having been booked in the co-main event against Li Jingliang.

With Ferguson making the weight at 170lbs and accepting the bump up to the main event – and almost certainly a significant pay increase to save the card – it left Li without a fight.

So, with Chimaev still willing to fight at a higher weight, he will now face Kevin Holland, with those two said to be at the centre of the backstage scuffle that ended the press conference. Holland had been preparing for a catchweight bout at 180lbs against Daniel Rodriguez, so he will not be outweighed by Chimaev when they contest the new co-main event.

That left Li and Rodriguez as the two remaining fighters to match up, but the problem is that Li had weighed in at 170, and Rodriguez came in at 180. In an Instagram post, Li said it is "no problem", and accepted the extremely tough upgraded opponent.

Charles Oliveira denied Justin Gaethje from claiming his vacated UFC lightweight championship, winning via submission in the first round at UFC 274 on Saturday.

Oliveira was stripped of the lightweight belt he held after missing weight, meaning only Gaethje could win the title on Saturday.

After a furious opening exchange, the 32-year-old secured an 11th consecutive victory, reaffirming his status as the most dominant fighter in the division.

Extending the UFC record for the most submission wins (16) and most finishes (19), the Brazilian made his status in the division clear despite the vacated title.

"There's something missing here. The champ has a name and his name is Charles Oliveira," he said post-fight.

"This is a message to the entire division. I'm a problem for the entire division, look at my team.

"Dana White, I don't care who you put in front of me. I will take them all on."

Gaethje came out the blocks quickly and landed some big shots but critically allowed his opponent to stand back up after he was knocked down.

Given that breathing room, Oliveira recovered immediately, planting a right-hand to get Gaethje down on the ground and then showed composure, not seeking ground-and-pound but a submission.

Gaethje gave up his back after wriggling out of an initial attempt at a triangle, and Oliveira took advantage from there with a rear-naked choke.

Esparza wins as Chandler makes vicious KO

In the co-main event, Carla Esparza claimed victory over Rose Namajunas in a controversial 47-48 49-46 48-47 split decision, to claim the UFC women's strawweight championship.

In what was a very tepid bout, Namajunas effectively left her fate and belt in the hands of the judges, allowing Esparza to make sporadic forays and takedowns.

It was very different to the other lightweight bout of the night, where Michael Chandler scored a breathtaking knockout win over Tony Ferguson in the second round.

After an exciting first round, Chandler ended the fight early with an explosive front kick, catching Ferguson on the chin.

Charles Oliveira made a narrow escape from the first round against Michael Chandler at UFC 262 before ending things in a hurry in the second. 

Oliveira (31-8) dropped Chandler with his first punch after the break and won by TKO 19 seconds into the second round to claim the UFC lightweight title in Houston. 

In his 28th UFC fight, the Brazilian earned his first strap, a belt left vacant when the unbeaten Khabib Nurmagomedov decided to retire. 

Chandler (22-6) had won the first round 10-8 on two judges' scorecards and 10-9 on the other, but he could not put Oliveira away. 

Once the 31-year-old had a chance to compose himself, he showed his class with a single shot. 

It was Oliveira's 17th career finish, moving him past Donald Cerrone for the most in UFC history. 

In the co-headlining bout, Beneil Dariush dominated Tony Ferguson to win unanimous decision.

The defeat was the third in a row for Ferguson (25-5), the former UFC lightweight interim champion, who previously lost by unanimous decision to Oliveira at UFC 256 in December. 

The Iran-born Dariush (21-4-1) said his seventh consecutive win should put him in the conversation in the lightweight ranks, but he plans to take the next several months off as his daughter is due to be born in June. 

Also on the card, Rogerio Bontorin defeated Matt Schnell and Katlyn Chookagian beat Viviane Araujo, both by unanimous decision, while Edson Barboza knocked out Shane Burgos at 1:16 in the third round. 

For the second time in as many UFC events, an undercard fight ended with an apparent broken limb. 

Brazilian veteran Jacare seemed to break his arm in losing by technical submission to Andre Muniz at 3:59 in Round 1. It was the first loss by submission for the 41-year-old Jacare (26-10).

At UFC 261 a fortnight earlier, Chris Weidman broke his leg landing a kick on Uriah Hall.