Serena Williams beats Karolina Pliskova to reach the US-open semifinal. Serena was trailing 4-2 in the first set and then hit back 6-4 6-4 to win the match. Williams gave birth to her daughter in last September and is trying to win her first Grand Slam trophy after that. Williams said she is playing free and she has nothing to prove. If she wins the trophy it will be her 24th major title in the career.