Injured Wawrinka pulls out of Federer clash

The ATP Finals' hopes of David Goffin stalled as the sixth seed lost to Reilly Opelka

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.