Second seeds Andy and Jamie Murray crashed out of the men's doubles in the first round after losing a thrilling contest to the Brazilian duo of Andre Sa and Thomaz Bellucci.
The British pair saved six match points during a second set tie-break but were eventually undone by a Bellucci winner which was aided by a net cord and sealed a 7-6 (8/6) 7-6 (16/14) victory in two hours and two minutes.
The shock result means the top two seeds in both doubles competitions have already been eliminated, with top seeds Nicolas Mahut and Pierre Hugues-Herbert of France having lost to Colombia's Juan Sebastian Cabal and Robert Farah.
Three-time champions Serena and Venus Williams suffered their first ever Olympic doubles loss to Czech pair Barbora Strycova and Lucie Safarova, while second seeds Kristina Mladenovic and Caroline Garcia of France were beaten by Japan's Eri Hozumi and Misaki Doi.
After losing the opening set, the Murray brothers broke in the first game of the second thanks to a double fault from Bellucci, but were unable to press home their advantage.
A second tie-break was required and turned into a classic as the British pair recovered from 6-3 down and went on to save three more match points, the fifth conceded by the worst volley Andy has arguably ever hit, but then saved by an ace from the Wimbledon champion.
The 29-year-old then produced a stunning backhand volley from an acute angle to save the sixth match point but could do nothing with the seventh, much to the delight of the partisan home crowd.
