David Haye's pre-fight bluffing backfired Saturday as bitter rival Wladimir Klitschko easily outpointed him in their disappointing heavyweight unification clash in rain-soaked Hamburg.

Haye plans to retire in October when he turns 31 and knew tonight was his chance to not only prove himself as a heavyweight but also establish a real legacy in the division as the man to end Klitschko's dominance.

But he failed at the soaking wet Imtech Arena to back up his distasteful and aggressive bravado by instead fighting defensively and losing with scores of 117-109, 118-108 and 116-110.

The event had threatened to be a damp squib with constant rainfall leaving most of ringside soaking wet, although the downpour eased by the first bell and a canopy over the ring itself seemed to be keeping the canvas dry.

Haye, who headed into the bout with a record of 25-1 with 23 knockouts, ended over two years of waiting when he finally came face to face with Klitschko (55-3, 49KOs).

After so much trash-talking and on-off negotiating, the two men were squaring off in what Haye labeled 'the biggest fight in boxing' and the most high-profile heavyweight clash since Lennox Lewis beat Mike Tyson in 2002.

The unification super-fight saw 30-year-old Haye putting his WBA heavyweight title on the line in a bid to snatch his Germany-based Ukrainian opponent's IBF, WBO and Ring magazine belts.

He did so as the clear betting underdog, conceding three inches in height, two stone in weight, years in experience and home advantage against a 35-year-old who had reigned since his last knockout defeat seven years ago.

Roared on by around 10,000 British fans among the approximately 40,000-strong crowd - who let themselves down by booing and jeering the Ukrainian national anthem.