Boxing WBC World heavyweight title fightFor all the pre-fight hype and analysis of the attributes of Vitali Klitschko and Danny Williams, the course of tonight's fight at the Mandalay Bay Hotel in Las Vegas will be dictated by an imponderable that cannot be fully assessed until the first bell sounds.

The question must be whether the Williams who tries to better the huge Ukrainian World Boxing Council champion is the man who fought with such ferocity to destroy Mike Tyson in July, or the angst-ridden loser who surrendered his British and Commonwealth titles so meekly to Michael Sprott back in January.

The Tyson-beater has a genuine chance of winning but the self-doubting Williams who lost at the Wembley Conference Centre will unquestionably be on the receiving end of a painful beating.

"Do I look nervous?" asked Williams as he mingled happily with the British fans at Thursday's weigh-in. "I'm ready, man. I've done the work and I'm going to win. My father always said I would be a world champion and this is my time."

The man who has sometimes seemed too gentle, caring and downright nice to be a professional fighter is approaching Klitschko with a seductive certainty of victory. Not only does he believe in the inevitability of a win, he also insists he has the power to floor Klitschko for the first time and win inside the 12-round championship distance.

Encouraging words have reached Williams from former champions including Evander Holyfield and Larry Holmes, who said: "Klitschko is not a good champion. He falls back as he throws his jab and is only awkward because he is so big. People build him up because he gave Lennox Lewis a hard fight, but Williams can win this. And he will be a different man after beating Tyson. Williams goes in knowing he is a winner and that makes a big difference."

Klitschko (33), has probably earned the right to be regarded as the leading light of a modern heavyweight division which may be as weak as at any time since Rocky Marciano retired almost 50 years ago. His only defeat apart from that by Lewis in a professional career that began in 1996 was when he was forced to quit against Chris Byrd four years ago with a damaged shoulder, an injury requiring surgery, and his power is underlined by a professional record which has 34 victories, set against his two defeats, with 33 of those wins inside the distance.

But it was his epic, bloody battle with Lewis in Los Angeles 18 months ago which finally established Klitschko's reputation. He fought well enough to rock Lewis several times and was winning according to the judges before facial cuts became too serious for him to be allowed to continue, leaving the referee to halt the contest after six rounds despite Klitschko's protests that he was fit to fight on.

Klitschko's performance against Lewis was heroic but it was also true that Lewis was a fighter in decline by the time he took the contest and he had been both ill-advised and ill-prepared to face Klitschko, having agreed to take the fight at short notice when his original opponent, the Canadian Kirk Johnson, pulled out claiming he was injured.

Last night Lewis chose his words carefully and did not endorse Williams's chances of springing a notable upset, saying instead that "it will be very difficult for him", adding that the first round might be crucial. Williams has promised to start fast and Lewis added that it is vital the British challenger quickly gets past Klitschko's jab and the inevitable powerful follow-up right crosses he will attempt to detonate on Williams's head.

Standing at more than 6ft 7in, Klitschko will try to win the fight at range, picking Williams off with his left lead before moving in with his more damaging right hand. But Williams (31), and his trainer, Jim McDonnell, believe they have the strategy to upset the methodical champion's rhythm.

Klitschko, they argue, is like many big fighters in that he is not as effective "inside"; in other words he fares badly when drawn into close-quarter exchanges.

"It may not be pretty," McDonnell has warned. And it seems certain that Williams will try to duck, bob and weave his way inside Klitschko's jab before using his 20lb weight advantage to maul and wear down the champion, testing what they believe to be Klitschko's suspect stamina. Williams tips the scale at a monster 19st 4lb.

"We planned for Danny to be heavy," said McDonnell. "He's not fat and he's comfortable at that weight. He is stronger than any fighter I have known and he is in the condition to go 12 rounds if he has to. Klitschko is going to find that he is out of his depth and Danny will take him under and drown him."

But Klitschko has vowed to make this a night of celebration for the people of Ukraine and it is difficult to visualise him being outboxed by a man who is six inches smaller and who, with the notable exception of his unexpected glory night against Tyson, has operated against a more modest level of opponent. Williams may have the puncher's chance but the more likely outcome is that Klitschko picks his man apart to score a stoppage win after about nine rounds.

TALE OF THE TAPE

DANNY WILLIAMSvVITALI KLITSCHKO

31AGE33

LondonBORNBelovodsk

6ft 1inHEIGHT6ft 7ins

19st4lbsWEIGHT17st 12lbs

79inREACH78in

43inCHEST(normal)46.5in

44.5inCHEST(expanded)48in

38inWAIST35.5in

17inBICEPS 17.5in

17inNECK18in

7.5inWRIST7.5in

17inCALF17in

28inTHIGH23in

12.5inFIST11in

11.5inFOREARM17in

32WON34

3LOST2

0DRAWS0

27KO'S33