Wimbledon champions Roger Federer and Serena Williams scored contrasting wins to progress into the second round of the Olympics on Saturday.
Federer survived a scare as the Wimbledon champion kicked off his bid for Olympic gold with a hard-fought 6-3, 5-7, 6-3 victory over Colombia's Alejandro Falla.
Meanwhile, Williams breezed through her first round match against Serbia's Jelena Jankovic on the opening day of the Olympic tennis with US first lady Michelle Obama cheering her on.
Obama watched from the players' box along with Williams' sister Venus as the fourth seed took just 61 minutes to see off former world number one Jankovic 6-3, 6-1. But it wasn't all smooth sailing for the seeds on the opening day of the tournament.
2011 French Open champion Na Li of China, Czech Republic's Tomas Berdych and Australian fifth seed Samantha Stosur all slipped on the Wimbledon grass.