The buyer of the 3.73 carat blue stone was British jeweller Laurence Graff, who also picked up a light pink diamond weighing 6.26 carats for 1.67 million francs, the auction house said.
In all, 423 of 508 lots on offer found new owners at Sotheby's three jewellery sales held in Geneva on Thursday night, netting a total 60 million francs, a statement said.
"We've had great success with important stones, with period pieces and particularly with jewels of noble provenance," said David Bennett, chairman of Sotheby's international jewellery department for Europe and the Middle East.
The star lot, the pear-shaped blue diamond graded "fancy vivid", the most intense colour, weighs just 3.73 carats and is mounted in platinum.
The price per carat was nearly $1.33 million, which exceeded the $1.32 million paid per carat for a 6.04 carat blue diamond it sold last October in Hong Kong, according to the auction house.
