The UFC's one-off event at The White House closed out with a highly-anticipated lightweight title unification bout between Ilia Topuria and Justin Gaethje.

Following adverse weather that required a one-hour delay to the event and it's opening bout between Diego Lopes and Steve Garcia, "UFC Freedom 250" took place on the South Lawn of The White House on Sunday night and featured five fights leading up to the two championship offerings that closed out the night.

After Ciryl Gane spoiled Alex Pereira's historic triple-champ bid in the night's interim heavyweight title fight, Gaethje and Topuria finally made their respective walks to the Octagon to close out the evening.

Justin Gaethje Upsets Ilia Topuria in "Fight of the Year" Contender

Entering the night with a perfect 17-0 record, Topuria previously won and defended the UFC featherweight belt before he moved up to lightweight at UFC 317 and knocked out Charles Oliveira to claim the division's vacant title.

The White House main event booking opposite Topuria marked Gaethje's third bid at undisuputed UFC gold, as he previously came up short in championship bouts against Oliveira and Khabib Nurmagomedov. "The Highlight" also carried the interim lightweight belt into his first title shot against Nurmagomedov, and he claimed that title for a second time at UFC 324 when he took a unanimous decision over Paddy Pimblett.

One of eight American fighters scheduled to compete at "UFC Freedom 250", Gaethje entered the night as a prohibitive underdog to the undefeated Topuria. It also looked to be a near-certainty that one of the two men would close the card out with a knockout, especially after the previous six fights at The White House all ended via strikes.

Topuria began to advance as soon as the fight started, keeping a high guard as Gaethje chipped away with jabs and even tried a surprise takedown attempt in the opening seconds. "El Matador" absorbed a number of significant shots from the interim champion as he remained committed to an uncharacteristically reckless approach, and the round ended with the two men trading massive punches along the fence.

Wearing some visible damage on his face, Topuria resumed his aggression in the second round and began mixing his punches up to both the head and body of Gaethje. "The Highlight" eventually hit the canvas after a barrage of body punches, and Topuria surprised fans by briefly looking for both a mounted triangle and an armbar before he settled into top position for the final minute of the second round.

Things got off to a bit of a slower start in the third frame with both men clearly fatigued, but Gaethje started to land his jab consistantly before throwing a huge right hand that put the undefeated champion on the mat. After fending off a choke attempt, Topuria worked back up to his feet but largely found himself playing defense for the remainder of what was a clear round for Gaethje.

Topuria's corner called for the doctor in between rounds and it looked like a near-certainty that the fight would be called off due to the damage "El Matador" had sustained to his eye. Shockingly, things the fourth round was allowed to start after the doctor initially advised that he not be allowed to continue. A gritty fourth round saw Topuria briefly end up in top position during the final minute before the two men went back to trading strikes, and a desperate takedown attempt from Topuria resulted in him ending the round on his knees.

Referee Marc Goddard immediately went to go check on Topuria as he made his way back to the corner, and it was one of the UFC star's cornermen that ultimately made the decision to call the fight off and hand Gaethje the biggest win of his career and the undisputed UFC lightweight belt.