Injured Wawrinka pulls out of Federer clash

Stan Wawrinka was forced to withdraw from Friday's Basel quarterfinal showdown against best friend Roger Federer with a back injury, just an hour after struggling past America's Frances Tiafoe in a gruelling second round clash.
Stefanos Tsitsipas reached his 13th quarterfinal of the year when he came back to claim a 6-7 (4/7), 6-2, 6-4 win over Lithuanian qualifier Ricardas Berankis. 
The ATP Finals' hopes of David Goffin stalled as the sixth seed lost to Reilly Opelka 6-7 (4/7), 7-6 (7/4), 7-5, with the young American sending down 29 aces in two and a half hours.
Roberto Bautista Agut, who sits one spot away from a London invitation, stayed in the chase as he defeated France's Richard Gasquet 6-2, 4-6, 6-3 and will next play Opelka.