Stan Wawrinka was leading match 6-4, 7-5, 2-1 Serbian world No 1 suffering with shoulder complaint Novak Djokovic’s US Open title defence came to a halt on Sunday when the Serb retired from his fourth-round match against Stan Wawrinka due to a shoulder injury. Wawrinka was leading 6-4, 7-5, 2-1...