World No.1 Cameron McEvoy qualified fastest for the 100m freestyle final at the Rio trials in Adelaide but veteran Matt Abood is primed to throw a spanner in the works.
Defending champion McEvoy clocked 48.09 seconds to top the time sheets but 29-year-old Abood (48.89) was surprisingly second fastest in a world class field.
The man expected to threaten the big names - world junior champion Kyle Chalmers (49.06) - was fourth fastest.
Dual world champion James Magnussen - back from shoulders surgery - was sixth fastest.
The race for the two 100m individual Rio spots was expected to come down to a showdown between McEvoy, Magnussen and Chalmers.
However, Abood - a veteran of four world titles campaigns - threw down the gauntlet with his fastest 100m time in three years.
Meanwhile, Emma McKeon set a new Commonwealth record when she claimed 200m freestyle gold.
She had already earned Rio selection by claiming the 100m butterfly title.
Bronte Barratt - the longest serving female member of an Australian swimming team - also qualified for Rio with 200m silver.
Barratt qualified for her third - and last - Olympics.
She has announced she will retire after Rio.
London Olympic bronze medallist Barratt, 27, has been a part of the national team since 2005.