It was First Lady Michelle Obama who laid down the sartorial gauntlet during yesterday's official Olympic festivities.
Mrs O looked spectacular in a sculpted white and silver J Mendel top and skirt at a formal reception at Buckingham Palace.
Samantha Cameron, however, stepped up to the fashion plate, in a geometric piece by UK-based designer Roksanda Ilincic for the opening ceremony.
Both women looked amazing. We declare the face-off a dead heat. What do you think?
And now for some more Sam Cam style...