LONDON, ENGLAND - NOVEMBER 13: Grigor Dimitrov (R) of Bulgaria celebrates victory in his Singles match as he shakes hands with Dominic Thiem of Austria during day two of the Nitto ATP World Tour Finals at O2 Arena on November 13, 2017 in London, England. (Photo by Clive Brunskill/Getty Images)
Getty Images

Getty Images Sport Clive Brunskill

LONDON, ENGLAND - NOVEMBER 13: Grigor Dimitrov of Bulgaria walks out for his Singles match against Dominic Thiem of Austria during day two of the Nitto ATP World Tour Finals at O2 Arena on November 13, 2017 in London, England. (Photo by Clive Brunskill/Getty Images)
Getty Images

Getty Images Sport Clive Brunskill

LONDON, ENGLAND - NOVEMBER 13: Dominic Thiem of Austria walks out for his Singles match against Grigor Dimitrov of Bulgaria during day two of the Nitto ATP World Tour Finals at O2 Arena on November 13, 2017 in London, England. (Photo by Julian Finney/Getty Images)
Getty Images

Getty Images Sport Julian Finney

LONDON, ENGLAND - NOVEMBER 13: Dominic Thiem of Austria serves in the Singles match against Grigor Dimitrov of Bulgaria during day two of the Nitto ATP World Tour Finals at O2 Arena on November 13, 2017 in London, England. (Photo by Julian Finney/Getty Images)
Getty Images

Getty Images Sport Julian Finney

LONDON, ENGLAND - NOVEMBER 13: Grigor Dimitrov of Bulgaria celebrates victory in his Singles match against Dominic Thiem of Austria during day two of the Nitto ATP World Tour Finals at O2 Arena on November 13, 2017 in London, England. (Photo by Clive Brunskill/Getty Images)
Getty Images

Getty Images Sport Clive Brunskill