Karsten Warholm of Norway celebrates after winning gold and setting a new world record REUTERS/Hannah Mckay.

TOKYO, Aug 3 (Reuters) - A world record had been predicted but Norway's Karsten Warholm had to utterly destroy it to hold off American Rai Benjamin and take gold on Tuesday in the men's 400 metres hurdles, in what will go down as one of the all-time great Olympic races.

Last month, Warholm broke Kevin Young's 29-year world mark with a time of 46.70 seconds but he blew his own record away with an astonishing 45.94 run.

Double world champion Warholm runs every race as if he is trying to break the world record and on home soil in Oslo last month he finally got Young's 1992 Barcelona Olympics mark off the books - and seemingly a weight off his shoulders.

Former 110m hurdles world record holder Colin Jackson added: "When you talk about world records, this is up there with Usain Bolt's time of 9.58 seconds in the 100m, up there with Flo Jo's 10.49 seconds in the 100m

"This is one of the most outstanding world records and I'm pretty sure that world record will outlive me."