Britain's Hannah Miley reached the 200m medley semi-finals as China's Ye Shiwen continued to dominate.
Ye was fastest in two minutes 8.90 secs, with Miley 10th-best in 2:12.27.
Michael Phelps also qualified for his 200m butterfly semis, but only fifth-fastest behind Austria's Dinko Jukic and American team-mate Tyler Clary.
reached the women's 200m freestyle semis, winning her heat ahead of French 400m gold medallist Camille Muffat.
McClatchey went through in a time of 1:58.03 but the 26-year-old faces stiff competition from Italy's Federica Pellegrini, Sweden's Sarah Sjostrom and American duo Missy Franklin and Allison Schmitt for medals.
The 23-year-old Clary landed himself in hot water when he criticised Phelps, 14 times an Olympic champion, for not working hard in the period following his eight Beijing 2008 gold medals.
Phelps said actions in London would speak louder than words, but it was Clary who delivered in the men's 200m fly heats. He qualified second-fastest for the semis in 1:54.96, with Phelps fifth-fastest in 1:55.53.
progressed for Britain, Roebuck narrowly missing out in a tie for 17th.
missed out on a women's 200m medley place, while
did not progress in the 200m freestyle.
Ye, only 16 years old, has already won the women's 400m individual medley title. She swam her final 50m in a faster split than 27-year-old Ryan Lochte did on his way to gold in the men's event.
Ye is the clear favourite to add a second gold over the shorter distance.
"It's nuts," said Miley. "It's just the amazing athlete she is.
"I can't do anything about that, except be awed and proud that I can race against her. The main thing was trying to get to the semi. In Beijing, I missed out on the final but this is a much tougher field."