World champion Rebecca Soni got her 2012 campaign underway at US Olympic trials in Omaha this morning with a 1:06.33 warm-up in the 100m breaststroke prelims.

The surprise was just behind her: 20-year-old Breeja Larson, who set a best of 1:08.08 at Austin this month, progress from a season best of 1:08.45 late last year, clocked 1:06.52. Larson had swum 100m three times before trials, the other two efforts 1:08.29 in January and 1:10.06 in May. World record holder Jessica Hardy was third through to semis in 1:07.25 as the first of three women on 1:07s.

In other action this morning, Missy Franklin and Rachel Bootsma cracked the minute in 100m backstroke heats, on 59.54 and 59.69, with Olympic champion Natalie Coughlin fifth through to semis on 1:00.71. The event holds the promise of Coughlin joining the triple champions club alongside Dawn Fraser and Krisztina Egerszegi after victories at Athens 2004 and Beijing 2008.

The stage is set for the next Ryan Lochte and Michael Phelps clash, Lochte on 1:48.14 in 200m freestyle heats, Charlie Houchin 0.01sec away, Phelps on 1:48.31. 

Lochte was back a little later for a 53.92 effort in the 100m backstroke as second fastest, Matt Grevers having laid down a 52.94 gauntlet two heats before. Third through was Nick Thoman, on 53.96. Lochte then scratched and will not race semis. It was not hard to work out before trials that not even Lochte would manage every round of every race he had entered and prosper as well as he is capable of prospering in all.  

His coach Gregg Troy said: "He really wants to swim the 100 but looking through the programme as the weeks pans out [and with a view to the Games proper] it really felt like this is not about how many he can swim  but how many he can swim really well."

The last event of the morning saw a tight match between Allison Schmitt and Kathleen Ledecky in heat 11, Schmitt getting the touch in 4:05.60, to 4:05.78 for Ledecky. The rest of the final qualified in a range of 4:07.91 to 4:10.38.

SwimNews will report live from Omaha this evening.