Olympic champion Kaylee McKeown is on track for another backstroke title at the Australian championships in Adelaide.
But celebrity swimmer Cody Simpson has been disqualified from the 100 metres freestyle at the national titles.
The pop star who has returned to the pool false-started in his heat on Saturday morning in Adelaide.
Simpson is a likely selection in the 100m butterfly for the Commonwealth Games in July-August after finishing third in the 'fly final on Thursday night.
While freestyle isn't his favoured stroke, he lined up in a heat including pacesetter William Yang on Saturday morning.
With Olympic 100m freestyle gold and silver medallist Kyle Chalmers not racing the event at the nationals, Yang and emerging 16-year-old Flynn Southam were fastest through the heats.
Yang and Southam clocked 48.62 seconds in separate heats with Jack Cartwright (48.66) next best.
Meanwhile, McKeown barely exerted herself while topping qualifying in the 200m backstroke.
McKeown breezed through her morning heat in Adelaide, which followed her 100m backstroke victory on Friday night.
The Olympic champion in both events, McKeown swam well within herself in her 200m backstroke heat and clocked two minutes 11.57 seconds.
The time was more than seven seconds slower than her Commonwealth record in the event set at last year's Olympic trials.
Bowen Gough was quickest in Saturday morning's men's 200m butterfly heats while Alexandria Perkins was fastest in the women's 50m butterfly heats.
In the men's 400m individual medley, Commonwealth record-holder Brendon Smith was the quickest through the heats.
