The Australian, who also triumphed in the 200m freestyle and 4x200m freestyle relay, was just 0.1sec outside his own world mark with a winning time of 52.25sec.
That was good enough for Poland-born Klim to take half a second out of the championship record established by his compatriot Geoff Huegill earlier in the day. Huegill, who beat his team-mate in the heats to break a championship best held for a few minutes by Frenchman Franck Esposito, had to settle for bronze in 52.90, with Sweden's Lars Frolander second in 52.79.
"I was feeling quite lethargic this morning after the last five days," Klim said. "I felt as though I didn't want to work anymore. But I recovered pretty well. And the butterfly always seems to bring something special out of me. I don't regard myself as one of the greats, I'd probably never look at myself like that, although people looking at the medal table might think that way."
No British swimmers reached an individual final yesterday, although James Hickman, fifth in the 200m butterfly, did win the consolation race in the 100m in 53.85.
In the 200m individual medley, Wu Yanyan claimed China's third gold of the championships, breaking former East German Petra Schneider's championship record set in 1972 by nearly a second in 2min 10.88sec. Chen Yan, winner of China's two other golds, was second with Slovakia's Martina Moravcova third.
Newcastle's Sue Rolph finished third in the consolation race in a time of 2:17.33, then completed a hat-trick of final appearances this week by taking over the freestyle leg of the 4x100m medley relay from Karen Pickering. The quartet, also including Sarah Price, Jaime King and Caroline Foot, came last, but moved up to seventh when Belgium were disqualified from the race won by the American team.
Britain only reached the final as the Chinese, shorn of a team because of the drug controversy surrounding four of their swimmers, did not turn up for the event.
American Kurt Grote took gold in the 200m breaststroke by just 0.02sec from Frenchman Jean-Christophe Sarnin, with Hungary's Olympic champion Norbert Rozsa third.
- Ian Gordon, PerthReuse content