US Open 2018: Juan Martin del Potro & Stan Wawrinka into third round

Third seed Juan Martin del Potro made comfortable progress to the US Open third round with a straight-set victory over American Denis Kudla.

The 2009 champion, back to his best after a series of injuries, won 6-3 6-1 7-6 (7-4) in one hour 56 minutes.

He will face Britain's Andy Murray or Spain's Fernando Verdasco for a place in the last 16.

Another former champion Stan Wawrinka beat French qualifier Ugo Humbert 7-6 (7-5) 4-6 6-3 7-5 to advance.

Ninth seed Dominic Thiem survived a scare to beat American Steve Johnson 6-7 (5-7) 6-3 5-7 6-4 6-1.

However, Greek 15th seed Stefanos Tsitsipas - who came into the tournament in good form after reaching the Rogers Cup final this month - was beaten 6-4 6-3 4-6 6-3 by unseeded Russian Daniil Medvedev.

World number one and defending champion Rafael Nadal is in action later against Canada's Vasek Pospisil.