World No.1 Serena Williams advanced to the semi-finals of the US Open, beating fifth seeded Romanian Simona Halep 6-2, 4-6, 6-3.The number one seed, who is seeking her seventh title in the tournament, will face in the semifinal Czech Karolina Pliskova, who beat Croatia's Ana Konjuh 6-2, 6-2, reports Efe.Williams, who has now won 309 matches in Grand Slam tournaments, two more than Swiss legend Roger Ferderer, used her physical strength and powerful serves to secure her win on Wednesday."I am very happy to have reached the semi-finals. I look forward to it, I have nothing to lose," Williams said after the match.