Hannah Miley and Caitlin McClatchey both safely negotiated their way through the heats of their respective events as the third day of swimming action got under way at the Aquatics Centre.
While the pair will race again on Monday evening, there was disappointment for Roberto Pavoni, Sophie Allen, Joe Roebuck and Rebecca Turner, with the latter two both finishing 17th, one spot outside qualification.
Miley was fifth in her favoured 400 metres individual medley on Saturday night and the 22-year-old returned to post the 10th fastest time of two minutes 12.27 seconds in the 200m.
Allen was devastated after finishing 21st in 2:14.72 and said: "My aim was to make the final so to not even make the semi-final, I'm gutted."
McClatchey eased into the 200m freestyle semi-finals in joint seventh but there was disappointment for Turner who missed out by just two hundredths of a second.
McClatchey is competing at her third Games having reached at least one final on each occasion, including a sixth-place finish in this event in Beijing.
The 26-year-old swam the anchor leg for the sprint relay that came fifth earlier this week and she looked impressive with her customary smooth technique to win her heat in 1:58.03.
Turner was in the same heat as defending champion Federica Pellegrini who, as in Beijing, finished fifth in the 400m. The Italian impressed this morning to lead the way in 1:57.16, 0.17secs ahead of Allison Schmitt, who set a textile world record at the US trials last month and who was second over 400m.
Turner, though, was always off the pace and her time of 1:58.98 was more than 1.3secs off the personal best she set in this pool earlier this year. It was only good enough for 17th as she was edged out by two hundredths of a second by Beijing silver medallist Sara Isakovic.
Roebuck was two hundredths of a second outside qualification in the 200m butterfly in 1:56.99, while Pavoni finished 20th in 1:57.55.