Fran Halsall and James Goddard both negotiated the first steps towards fulfilling their Olympic swimming dreams, while the women's 4x200 metres freestyle - minus Rebecca Adlington - qualified for Wednesday evening's final at the Aquatics Centre.
Where possible British Swimming will rest swimmers who have individual races to prepare for, and the Bill Furniss-coached star takes to the water for the 800m freestyle heats on Thursday morning.
Caitlin McClatchey, Rebecca Turner and Eleanor Faulkner have all gone quicker this year and the trio, along with Adlington's close friend Jo Jackson, made up the squad that qualified seventh overall in seven minutes 54.31 seconds.
Jackson, who failed to make the 400m freestyle final four years after picking up the bronze medal, said: "It's been a tough week. It hasn't gone to plan. I was grateful they put me in the heat to give me another shot after the 400. The 400 didn't go to plan. I was absolutely gutted but I came out there for the team today and hopefully I did a good job."
Halsall's time of 54.02 in the 100m freestyle saw her through seventh overall. The 22-year-old said recently she prized a gold in what she described as the blue riband event above anything else. Team-mate Amy Smith also made it through in 13th in 54.37, with China's Yi Tang quickest.
For Goddard, London represents the last chance of an Olympic medal after finishing a heartbreaking fourth in the 200m backstroke in Athens and sixth in the 200m individual medley four years ago.
The Stockport ITC swimmer is concentrating solely on the medley given the proximity of the events in the schedule, especially in relation to an ongoing shoulder problem. The event has been billed as a showdown between Phelps and fellow American Ryan Lochte, although Beijing silver medallist Laszlo Cseh will be looking to gatecrash the party.
Goddard was fourth behind the trio at last year's World Championships and second to the Hungarian in his heat in 1:58.56, sixth overall into tonight's semis.
Joe Roebuck was ill only a few weeks ago but he also made it through in 15th in 2:00.04, and he said: "I am just really happy to be here, so to be coming back tonight, I can't wait to walk out there."
Marco Loughran and Chris Walker-Hebborn failed to make it through to the 200m backstroke semis, while Stacey Tadd was two places off qualification in 18th in the 200m breaststroke.