Serena Williams overcame her sister Venus in three sets 6-2, 1-6, 6-3 at the ongoing US Open to reach the Semi Finals. This puts Serena two wins away from her first calendar Grand Slam. The world No.1 who faced Venus for the 27th time said, It's going against your best friend and the greatest competitor, so it was really difficult. Venus is a former world No.1 player. She became the first black American woman to achieve this in the Open Era. She has 7 Grand Slam singles- 5 Wimbledon and 2 US Open titles and a Singles Olympic Gold. Venus is regarded as the best grass court player of her generation and is considered as one of the all-time greats of women's tennis. Serena Williams is the current world No.1 player of women's tennis. With 21 Grand Slam singles titles (6 Australian Open, 3 French Open, 6 Wimbledon and 6 US Open), she is just behind Steffi Graf (22) in winning most number of Grand slams in Open Era. She is the reigning champion of the Australian Open, French Open, Wimbledon, U.S. Open and WTA Tour Championships. Serena and Venus have won 13 Grand Slam doubles titles- 4 Australian Open, 2 French Open, 5 Wimbledon and 2 US Open, playing alongside each other and are undefeated in Grand Slam finals. Serena and Venus are the most recent players to have held all four Grand Slam women's doubles titles simultaneously (2009\u201310). The Williams sisters have won three Olympic doubles Gold medals. Venus and Serena Williams have met 27 times since 1998, 14 in Grand Slam events and 13 times in other tournaments. They have met in eight Grand Slam tournament finals, with Serena winning six times. Overall, Serena is 16\u201311 against her sister. It is a rivalry that in terms of importance and longevity compares with Chris Evert- Martina Navratilova and Steffi Graf- Monica Seles. Amelie Mauresmo (former world No.1 who coaches Andy Murray) and others suggested years ago that matches between the sisters might be fixed. The most controversial match between the two came in 2001 at Indian Wells. After losing to Venus in quarterfinals, Elena Dementieva, a fellow professional player suggested that Richard Williams, the father of Williams sisters decided the results between the two sisters. Serena Williams overcame her sister Venus in three sets 6-2, 1-6, 6-3 at the ongoing US Open to reach the Semi Finals. This puts Serena two wins away from her first calendar Grand Slam. The world No.1 who faced Venus for the 27th time said, It's going against your best friend and the greatest competitor, so it was really difficult. Calendar Grand Slam or simply Grand Slam refers to the achievement of winning all four major championships in a single calendar year. Steffi Graf was the last player to have won it in 1988.