Last 16 battles loom as Kyrgios forced out

    Nick Kyrgios was forced to retire from the US Open through injury.

    Story highlights

    • Kyrgios out through injury
    • Juan Martin del Potro into fourth round
    • Djokovic back in action Sunday

    (CNN)Rising Australian star Nick Kyrgios was forced to retire from the US Open after three sets of his third round match.

    Kyrgios was behind in the tie with Ukrainian Illya Marchenko but decided to concede after what the official US Open website said was a hip injury.
      It hands Marchenko a fourth round tie with the number three seed Stan Wawrinka, who survived a match point against him to win in five sets against Britain's Dan Evans.
      "I'm pretty disappointed," Kyrgios told reporters. "I don't like to retire. It's probably like the second or third time I've done it. It's never easy."
      Some of the other stars of the men's game cruised through into the last 16.
      Silver medalist at the Rio Games, Juan Martin del Potro, beat Spain's David Ferrer 7-6 (7/3) 6-2 6-3 to make his first major fourth round since Wimbledon three years ago.
      The Argentinian has battled against terrible injury problems but is hitting the kind of form that won him the US Open in 2009 when he beat Roger Federer.
      "I didn't expect to be in the second week of this tournament," Del Potro told reporters.
      "I didn't expect to get a medal in Rio. I didn't expect to play at this level in this part of the year...but I think I'm surprised with my level at the moment."
      Some of the top seeds are back in action Sunday. Rafael Nadal (4) is first on court in his fourth round match against Lucas Pouille, and top seed Novak Djokovic has a fourth round match against Briton Kyle Edmund. France's Jo-Wilfried Tsonga (9) takes on American Jack Sock.
      In the women's game, Caroline Wozniacki plays American Madison Keys (8), and Wimbledon and Rio finalist Angelique Kerber (2) faces Czech player Petra Kvitova (14).