Gaethje was congratulated by President Trump after the event
ByPaul Battison
BBC Sport Journalist
Justin Gaethje provided the perfect ending for American fans at the White House as he shocked Ilia Topuria to win the UFC undisputed lightweight title.
American Gaethje, 37, shrugged off his underdog tag as he stopped Topuria at the end of the fourth round to become undisputed champion for the first time.
Gaethje hurt Topuria multiple times in a brutal contest as the Georgian-Spaniard retired on his stool before the fifth round for the first defeat of his 18-fight career.
The one-of-a-kind show, billed as UFC Freedom 250, took place on US President Donald Trump's 80th birthday as part of celebrations to mark 250 years of American independence.
After securing victory, which UFC commentator Joe Rogan called "one of the biggest upsets in the history of the sport", Gaethje did his signature backflip from the top of the cage before shaking hands with Trump.
In a rousing post-fight interview, Gaethje compared his underdog status to Americans who once fought for their country's independence.
"I'm from America, 250 years ago we were way bigger than 6-1 dogs, and look at us thriving now," said Gaethje.
"To all the current, former and future military service members, thank you so much."
In the co-main event, Ciryl Gane ended Alex Pereira's hopes of becoming the UFC's first three-division champion with a second-round stoppage in their interim heavyweight title fight.
Gaethje wins long-awaited title
The event was held to celebrate 250 years of American independence
The White House has hosted recreational sports and events before, but the event on the South Lawn marked the first professional live sporting show to take place on the grounds.
There were worries in the build-up that thunderstorms in Washington DC could cause delays, and although rain postponed the start of the event by around half an hour, it ran smoothly from there.
The show opened with President Trump and beaming UFC president Dana White walking through the White House to the Truman Balcony overlooking the octagon, before a rendition of the national anthem took place while US Air Force jets cruised overhead.
About 4,300 people watched the event on the South Lawn, most of whom were members of the US military, who chanted "USA" in support of the American fighters on the card.
Trump watched the event octagon-side alongside White, while the United States Marine Band serenaded fighters during their walkouts, which started from inside the White House.
Gaethje started his walkout in the Oval Office, where he took a moment to soak in the occasion, before walking past portraits of previous US presidents.
Topuria, who is a former champion at featherweight before he moved up to claim the lightweight belt, struggled to impose the power he has shown in previous bouts as Gaethje traded shots in the first round.
Although Topuria dropped Gaethje with a number of stinging body shots in the second round, the American took control from there, to the delight of the fans at octagon-side and 85,000 watching in the nearby Ellipse park.
He knocked Topuria down with a huge right hand and continued to punish him with uppercuts and knees, causing his opponent's bloodied face to start to swell.
The doctor was called in to look at Topuria before the fourth round, and although he bravely fought on, his corner retired him before the final round with the 29-year-old unable to take any more damage.
Victory means Gaethje, who is considered one of the most exciting fighters in UFC history, claimed his first undisputed title at the third attempt as he was rewarded with a commemorative red, white and blue belt.
"I am made for this moment, this sport was made for me. I'm the most exciting guy that's ever been in this cage," he added.
Justin Gaethje has won 28 of his 33 professional fights
Gane ends Pereira's three-belt dream
After winning titles at middleweight and light-heavyweight, Pereira was looking to make UFC history with a title in a third division but was outclassed by Gane.
Gane, 36, has navigated numerous fights throughout his career with his fluid movement and it once again paid dividends against Pereira.
After hurting the Brazilian with jabs and body kicks in the first round before escaping out of harm's way, Gane landed the decisive strike.
As Pereira stepped in, Gane dropped the 38-year-old with a perfectly timed jab and although he got back to his feet, the referee waved off the contest as the Frenchman overwhelmed his dazed opponent.
Victory meant Gane became a two-time interim heavyweight champion in his first fight since a bout against British champion Tom Aspinall in October.
That fight was deemed a no contest because of repeated eye pokes from Gane which left Aspinall unable to continue, and he called for a rematch in October.
"I just want to see thank you to Dana and the UFC, thank you to Pereira," said Gane.