Dubai - Ryan Lochte was set to bid for his third gold medal of the World Short Course Championships later Friday after winning the 200m individual medley heat.
The US star, who set a 1:53.39 in the heats session ahead of Rogan Markus of Austria and Henrique Rodrigues of Brazil, admitted to feeling tired after his world record-breaking performance in Thursday's 400m individual medley.
"I just wanted to expend as little energy as possible," he said.
"I knew I'd been in a race yesterday and felt a little tired but that was a good morning swim. It's going to be tight. There are at least two or three guys who will be very close.
"I'm just going to go out there and race tough."
Rivals Rebecca Soni of the US and Leisel Jones of Australia both won through to the women's 100m breaststroke semi-final, with Soni qualifying first in 1:04.65 and Jones in third in 1:05.36. China's Ji Liping was second in 1:05.32
Soni, who won gold in the 50m breaststroke on Thursday, said her success in the shorter event had helped her adjust to short course metres.
"I got used to the 50m after the first two days and I had really good rhythm in the first 50m of that race," she said.
"I'm happy with my result. I was really surprised with winning gold yesterday, I'm really happy."
Jones said she didn't push the pace.
"It was amazing and really cruisey, I just did enough to get to the semi-final as there were a few fast swimmers there."
Championship records kept falling with Russia's Stanislav Donets, fresh from winning gold in the 100m backstroke on Thursday, leading qualification for the 50m backstroke semi in a championship record of 23.45.
The Chinese women also set a new championship record in the 4x100m medley relay heat with a 3:50.69 mark and Daniel Gyurta of Hungary's 2:04.46 swim in the men's 200m breaststroke was a new championship record.
Japan's Naoya Tomita had set a new mark of 2:04.93 in the preceding heat which Gyurta, the world record holder then eclipsed in his own heat.