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GLASGOW, SCOTLAND - SEPTEMBER 16: Andy Murray of Great Britain hits a forehand during his singles match against Juan Martin del Potro of Argentina during day one of the Davis Cup Semi Final between Great Britain and Argentina at Emirates Arena on September 16, 2016 in Glasgow, Scotland. (Photo by Clive Brunskill/Getty Images)

GLASGOW, SCOTLAND - SEPTEMBER 16:  Andy Murray of Great Britain hits a forehand during his singles match against Juan Martin del Potro of Argentina during day one of the Davis Cup Semi Final between Great Britain and Argentina at Emirates Arena on September 16, 2016 in Glasgow, Scotland.  (Photo by Clive Brunskill/Getty Images)