Laura Robson lost 6-7, 3-6 and Heather Watson lost 3-6, 2-6.
In the longest ever Olympic tennis match Jo-Wilfried Tsonga beat Canadian Milos Raonic 6-3 3-6 25-23.
Key matches today:
Federer v Istomin 12.00 noon scheduled start
Murray v Baghdatis 4.00 pm
Djokovic v Hewitt 2.00 pm
Azarenka v Petrova 2.00 pm
Sharapova v Lisicki 4.00 pm
Serena Williams v Zvonareva 12.00 noon