Daniil Medvedev launched the defence of his US Open crown on Monday with a straight sets victory over lowly ranked American Stefan Kozlov. World number one Medvedev, bidding to become the first man to successfully defend the US Open since Roger Federer in 2008, eased into the second round with a 6-2, 6-4, 6-0 win in 2hrs 1min. Victory was sweet for Medvedev, who revealed he had regularly struggled to beat Kozlov when the two played at junior level. "He was almost impossible to beat," said the Russian, citing one encounter where his opponent "destroyed me."