The details of what happened at the event can be found in the story. You can watch the main card here and the highlights on the iPlayer.
In the second fight of his career, Brazil's Patricio Pitbull avenged his first career loss to win the title for the third time.
The bout was a repeat of the grand prix final, where McKee submitted Pitbull to win the title and the $1m tournament prize.
The three cageside judges scored the fight 49-46, 48-47, 48-47 in favor of the Brazilian, who had won the first fight by unanimous decision.
The bout started in a cagey fashion, with the American looking to score from distance and the Cuban looking to catch him on his way in. In the second round, Pitbull was able to find a home for his shots, and he landed a pair of eye-catching body shots towards the end of the round, before returning to the corner with his hand raised.
The third round was the best. He stunned McKee with a big right hand, then, moments later, locked up a tight triangle choke that briefly appeared to have the champion in trouble before he escaped.
The three judges all scored the bout for Pitbull, despite the fact that McKee tried to up his work-rate in the final two rounds.
He is a tough guy. He is a great opponent. "It was a hard fight for me, and I changed my mindset from the first bout to the second one."
I came in peace that day. I came for war today and am bringing the belt home.
There was confusion in the night's co-main event, where the light heavyweight title bout between champion Vadim Nemkov and top contenderCorey Anderson was ruled a no contest after an accidental clash of heads.
The title was on the line when the pair met in the final of the grand prix. Both men left disappointed after an unfortunate incident.
After a close opening round, Anderson, 32, took over in the second and third rounds with his dominant wrestling giving him a clear edge over his opponent.
The champion was left with a huge gash above his left eye when the pair clashed heads on the ground.
After referee Frank Trigg stopped the bout with seven seconds remaining in the round and brought in the cageside doctor to check out the injury, the bout was waved off. The contest was ruled a no contest because the bout did not complete three full rounds.
It meant that the grand prix was unresolved. The two tournament finalist are likely to face off again later this year.
In the main card opener, Vassell, an English contender, got one step closer to a shot at the title with a come-from-behind knockout of Tim Johnson.
Vassell, 38, looked to be in big trouble early in the first round when he was caught clean with a big right hand from Johnson, 37, that sent him to the canvas.
Despite the American's best efforts to finish the fight, Vassell scrambled his way out of trouble before turning things around.
Vassell took Johnson's back, postured up, then unloaded a barrage of heavy ground and pound on the American to complete a remarkable comeback and force the first round to be stopped.
After his victory, Vassell called on Scott Coker to give him a shot at the title held by American Ryan Bader or a fight against one of the top contender.
Vassell said he was the ground guy. From the UK. No wrestling background came to the US and the rest is history.
We all know that I want that title fight. So, title fight.
If I don't get that... There is a person named Moldavsky.
Vassell's win improved his record to 23-8 and extended his winning streak to four, with his victory over Johnson adding to prior successes against Sergei Kharitonov, Ronny Markes and Tyrell Fortune.