Durban - Chad le Clos moved effortlessly through his heats on the fourth morning of the South African National Aquatic Championships, reaching a semi-final and final, while Franko Jonker was the most impressive among the women in Durban on Thursday.
The Olympic gold medallist was the second fastest qualifier on his way to the 100 metres butterfly semi-finals with a time of 55.04 seconds, with Ryan Coetzee (54.54) quickest and Joshua Steyn (55.44) third.
Le Clos was then third fastest in the 400m individual medley after a casual swim saw him touch the wall in four minutes 33.39 seconds (4:33.39).
Sebastien Rousseau flew through as the top swimmer with a time of 4:20.98 - over 11 seconds ahead of Michael Meyer (4:32.16) - at the Kings Park Aquatics Centre.
Le Clos' younger brother, 15-year-old Jordan, will also line up in the final later on Thursday after a time of 4:41.27.
Other swimmers to top the heats on day four of the nationals, which is doubling as the official qualification event for the 2014 Commonwealth Games in Glasgow, were Cameron van der Burgh and Darren Murray.
Van der Burgh, Olympic gold medallist and world record-holder in the 100m breaststroke, was the fastest qualifier across 50m with 28.51.
Jared Pike (28.71) came second and Brad Tandy (28.81) was third.
In the 100m backstroke, Murray posted a time of 56.22 to end ahead of Ricky Ellis (56.41) and Bryan Gray (56.43).
Jonker, meanwhile, was marginally outside the 1:08.63 qualification time on her way to winning the women's 100m breaststroke in a time of 1:09.00.
Tara Nicholas (1:09.09) came second, with Justine Macfarlane (1:11.68) third.
In the other two events of the morning, Lehesta Kemp (30.05) was fastest in the 50m backstroke and second quickest in the 50m freestyle with a time of 26.21. She finished behind Trudi Maree (25.85) in the latter event.
All swimmers must record the stipulated qualifying times this week if they want to have a chance of making the Team South Africa squad for the July 23 to August 3 spectacle in Scotland.