Fellow Briton Adam Peaty took gold to make it a highly successful race for Team GB in Kazan. South Africa’s Cameron van der Burgh was second.
Murdoch, consigned to lane eight as the slowest of the finalists, could scarcely believe he had won a medal in an event which is not his strongest. In doing so he set a new Scottish record time of 59.09 seconds. Peaty overhauled Van der Burgh in the final 25m to win in 58.52sec with the South African seven-hundreths of a second behind.
“I can’t believe I got my hands on that world medal,” Murdoch said. “I had a bit of a blunder last night [in qualifying] but I came into this final relaxed.”
The Scot, whose favoured 200m breaststroke takes place on Thursday and Friday, felt that being in the outside lane helped him: “I couldn’t see them and they couldn’t see me,” he said of his rivals.
The Stirling University swimmer, who beat Michael Jamieson to win 200m gold at last summer’s Commonwealth Games, added: “I still feel a little bit out of my comfort zone at the faster [stroke] rates.
“I’m the fastest I’ve ever been. That gives me a lot of confidence going into next year for the front end of that 200.”
Peaty, meanwhile, becomes the first British world champion in the 100m breaststroke since David Wilkie won both the 100m and 200m in 1975.
It was the latest in a series of successes for Peaty, boosting hopes for next summer’s Olympic Games in Rio de Janeiro.
He won gold in the 100m breaststroke at Glasgow 2014 and four gold medals in the 2014 European Championships in Berlin, including in the 50m and 100m breaststroke.
He is also world record holder over 50m and 100m breaststroke. The 50m breaststroke begins in Kazan today with the final tomorrow.
Peaty had set a championship record en route to the 100m final and delivered gold in a discipline in which Britain has pedigree through Duncan Goodhew, Adrian Moorhouse, Nick Gillingham and Jamieson.
Peaty told BBC Sport: “I wasn’t going for my world record, I was just going for gold. I knew I had some catching up to do but I kept fighting right to the end.”
Scotland’s Hannah Miley finished outside the medals in the women’s 200m individual medley. The Inverurie swimmer was fifth in a race won by Hungary’s Katinka Hosszu in a world record time of 2mins 06.12secs. That bettered the old mark of 2:06.15 set by American Ariana Kukors at the 2009 worlds in Rome at a time when swimmers were setting a slew of world records in rubber suits that were eventually banned.
Kanako Watanabe of Japan was second (2:08.45), with Britain’s Siobhan Maria O’Connnor third (2:08.77). Miley’s time was 2:10.19.
Sarah Sjostrom of Sweden beat her own world record in the 100m butterfly to win gold. Sjostrom first broke the mark set by American Dana Vollmer at the 2012 London Olympics in the semi-finals on Sunday. In yesterday’s final, she won by a body length, touching in 55.64 seconds. She dipped a hundredth of a second lower than her mark a day earlier while finishing 1.41 seconds ahead of Jeanette Ottesen of Denmark. Lu Ying of China took bronze.
American teenager Katie Ledecky also bettered her own world record, in the 1,500 freestyle preliminaries.