McKeon's clip of 24.02 was the quickest of the 11 heats, with Cate Campbell qualifying 3rd quickest with 24.15.
Both the Australians bushed retired Swedish 50m satellite grounds holder Sarah Sjoestroem who swam a 24.26.
China's Zhang Yufei, who took retired golden successful the 200m butterfly and the 4x200m freestyle relay, qualified sixth quickest for the semi-finals with a 24.36 swim.
Unfortunately, determination was nary specified occurrence for Australia successful the men's 50m freestyle heats, with Cameron McEvoy failing to suffice for the semi-finals.
McEvoy's 22.31 ranked 29th successful the heats, overmuch slower than the 21.89 helium swam successful the 50m semi-finals successful Rio 5 years ago.
American prima Caeleb Dressel qualified quickest for the semi-finals with 21.32 up of Rio metallic medallist Florent Manaudou (France) who swam a 21.65.
Brazil's Bruno Fratus, who reached the 50m freestyle last successful Rio was fourth-quickest successful the heats with 21.67.
There was besides heartbreak for Australia successful the men's 1500m freestyle heats with Jack McLoughlin incapable to suffice for the last aft finishing 10th successful the heats with a clip of 14:56.98.
Ukraine's Mykhailo Romanchuk led each qualifiers with a clip of 14:45.99, beating retired USA's Robert Finke (14:47.20) and Germany's Florian Wellbrock (14:48.53).
There was much luck successful some the men's and women's 4 x 100m medley relay, with the women's squad qualifying third-fastest for the final, portion the men's squad finished sixth fastest.
Australia looked to beryllium successful information of missing the last earlier a superb last 50m from anchor Kyle Chalmers (22.73) allowed the squad to decorativeness 3rd successful its heat.