One teenage star beat the new kid on the block as Coco Gauff knocked 16-year-old Mirra Andreeva out of the US Open.Gauff, who burst onto the scene when she beat Venus Williams on her way to the fourth round at Wimbledon aged 15, ousted the Russian rookie 6-3 6-2.The sixth seed, still only 19, had to come from behind to beat Laura Siegemund in a drama-filled three-setter on Monday, but she had a far more gentle workout this time on Arthur Ashe.Gauff is fast becoming a live contender for the title this year having won 13 of her 14 matches since losing in the Wimbledon first round to fellow American Sofia Kenin.She lost a first-set tie-break against Andreeva at this year's French Open but came back to win in three.Gauff said: "I just learned then to be aggressive, because if you give her something she is going to take advantage."She has a great future in front of her – I think she is going to be back on this stage many more times."There was another home success in New York when Taylor Townsend beat Brazilian 19th seed Beatriz Haddad Maia 7-6 (7-1) 7-5.