4) Lucie Safarova and Barbora Strycova win against Williams sisters
Before their match against Safarova and Strycova of Czech Republic, the Williams sisters had a 100% record in the Olympics. They had played 15 games together and had never seen the face of defeat which meant they had three Olympic Gold medals already in their kitty. In their first match at Rio, the sisters were up against a pair who had not won anything before together.
But history changed for both the pairs at Rio as the tennis giants were served a defeat in straight sets. The two Czech women were not even supposed to play together and were paired only when Karolina Pliskova withdrew from the tournament at the last moment.
After bringing the top ranked pair down to earth, the unseeded Czech pair shook up quite a few names on their way to the semis and eventually earned a surprise Bronze. However, the win over the Williams sisters in the first round would probably sit a place higher than their Bronze achievement.