Watson loses to Williams in thriller, BBC Sport show mastery of simple mathematics

'British number one Heather Watson gave top seed Serena Williams a huge scare before losing a thrilling third-round match at Wimbledon.

The 23-year-old battled back from a set down, winning six straight games from 3-3 in the second set.

Watson served for the match at 5-4 in the decider but five-time Wimbledon champion Williams recovered to win 6-2 4-6 7-5 in two hours and 15 minutes.'

Can you spot the mathematical mistake? 

If Heather Watson won six straight games from 3-3 in the second set, how did she win that second set 6-4 rather than 6-3?

The BBC article is here http://www.bbc.com/sport/tennis/33390494