With France’s world champion Leon Marchand skipping Doha, Texas University student Johnston won his heat in 4:12.51s to upstage US teammate and defending silver medallist Carson Foster, who qualified fourth.

Britain’s former European champion Max Litchfield was second fastest in the heats, only 0.03s slower than Johnston, while Japan’s Olympic bronze medallist Daiya Seto was third.

The women’s 400m medley is wide open, with none of the medallists from last July’s World Championships in Fukuoka competing.

Former short course world champion Cieplucha swam 4:40.80s to top the timesheets ahead of Serbia’s Anja Crevar.

The US are top seeds for the men’s medley relay final later today, ahead of the Netherlands and third seed Spain.

Canada took top seed for the women’s medley relay ahead of Sweden and Australia.

Eight gold medals will be awarded in the final evening session later today, headlined by Sarah Sjostrom’s 50m freestyle title defence.

The men’s 1,500m freestyle gold will also be up for grabs, along with non-Olympic titles for the men’s 50m backstroke and the women’s 50m breaststroke.