Angelique Kerber was the biggest name to fall from the women's draw in the early stages of the first day of the US Open as she was upset by Kristina Mladenovic. Mladenovic suffered back spasms that twice required medical attention in a second set dominated by the German but recovered in the decider, breaking Kerber in the first game to seize the momentum. She crushed her 46th winner, a forehand from the baseline, on match point to end the nearly two-and-a-half-hour encounter and win 7-5, 0-6, 6-4. The outcome registered as a surprise but not quite a shock as Kerber, in recent months, has not looked like the player who won both the US and the Australian Opens in 2016 before capturing the Wimbledon championship last year. "The first rounds are always not so easy especially since I played not so well in the last few weeks," Kerber admitted. The unseeded Diyas, from Kazakhstan, took five straight games in the first set, as the world No 2 committed a string of unforced errors and got in just 25 per cent of her first serves. French Open champion Barty was able to stop the pain midway through the second set, converting on a crucial break-point opportunity to take a 5-3 lead and reverse the momentum in what had been a one-sided match. Johanna Konta was forced to work by Daria Kasatkina but eventually won 6-4, 4-6, 6-2 to win her first match on hard court all summer. Konta cruised through the opening set against the world No 42 and looked set for a comfortable victory but dropped her level to lose the second and her composure midway through the match. However, she found her range again in the final set as Kasatkina's serve fell apart and claimed victory after two hours and four minutes. Venus Williams and Maria Sakkari were both big winners, progressing through for the loss of just one game each with Zheng Sai-Sai and Camila Giorgi the unfortuante losers, while No 3 seed Karolina Pliskova needed two tie-breaks to see off Tereza Martincova. The headline bout of the day in the women's draw – Serena Williams vs Maria Sharapova – is set for the night session.