By Chris Summers
BBC Sport at ringside in LA
Relief showed all over Lennox Lewis's face when, after six thrilling rounds, ringside doctor Paul Wallace decided challenger Vitali Klitschko could not fight on.
Dr Wallace decided the Ukrainian could not see out of his left eye, because of a disfiguring cut to his eyelid which occurred in the third round.
Klitschko later claimed the cut was caused by a headbutt - something Lewis dismissed with contempt - but it appeared the damage was actually caused by an overhand right.
The media room after the fight was abuzz with talk of conspiracy theories - that the unsatisfactory ending had been cooked up by Lewis's TV paymasters HBO with a view to a lucrative rematch on pay-per-view in the autumn.
Such talk seemed far-fetched, especially when you saw Klitschko's cut eyelid on giant close-ups shown on screens above the auditorium between rounds.
Dr Wallace explained: "The cut interfered with the boxer's ability to protect himself. He had to move his head so the lid was out of the way.
"If he could not see a person he couldn't see a punch. The laceration became a danger to him."
He said Klitschko's cut men did a wonderful job to stem the blood but he said the cut had got so bad he had no choice but to stop the fight.
Klitschko was furious with the stoppage and claimed he was perfectly able to see.
Next time around, without the ring rust and with proper preparation, Lennox will do a number on him
He said he believed Lewis was out of condition and his gameplan was to outlast the champion over 12 rounds or stop him late on.
Lewis, for his part, claimed he would have knocked out Klitschko in another couple of rounds and he claimed the stoppage had actually "cheated" him of a spectacular victory.
Afterwards Audley Harrison, who was at ringside, told this website there was no way the fight could go on.
Harrison said being inactive for a year had not done Lewis any favours and he said ring rust was to blame for the champ's initially sluggish performance.
"No matter how much sparring you do, if you've been out of the ring for a year ring rust hits us all, especially Lewis whose style is all about finding his rhythm."
As for a rematch, Harrison reckoned it would suit Lewis more than Klitschko.
"That was the best of Klitschko you saw tonight. Next time around, without the ring rust and with proper preparation, Lennox will do a number on him," said the Olympic gold medallist.
Lewis struggled to contain Klitschko from the start
The fight, in LA's Staples Center, was the first world title clash in the City of Angels since 1958 and was worth the wait.
Nearly 16,000 fight fans roared their appreciation as the two big men slugged it out.
The second round, in particular, was a classic with Klitschko catching Lewis early on with a huge right.
Lewis held on and smiled but there was no doubt he was hurt, although he denied it later.
But the champ came back with a huge shot of his own and one American journalist standing near me shouted out: "We've got ourselves a fight, baby."
Late in the round Klitschko continued to connect with several huge punches and Lewis looked out on his feet.
He forgot all about covering up and was drawn into a brawl.
But the fight's entire complexion changed in the third when Lewis opened up that horrific cut with an overhand right.
It boosted his confidence but the Hamburg-based Ukrainian continued to give him trouble and was ahead on all three judges' scorecards at the end of the sixth.
A rematch in the autumn is now inevitable and it is a fight which already had fight fans licking their lips.
At the post-fight press conference Lewis said he would happily give Klitschko a rematch if the money was right.
He said: "I'm happy to give him a rematch because I will bust up the other side of his face as well."
His trainer, Emmanuel Steward, admitted it was not one of Lewis's best performances.
But he said he felt the champ's experience in big fights would have led to him knocking out Klitschko if the fight had been allowed to go on.
As for Klitschko, and his belligerent German promoter Klaus Peter Kohl, they insisted their man was winning the fight and would have won.
Speaking in passable English, the giant Ukrainian - who had reportedly received 60 stitches in his cut face - he said: "I was ahead on points and I want to be champion now or later."