Djokovic , 29 , has qualified for the semi-finals after winning his first two group matches at London 's O2 Arena .
Murray should also make the last four with two victories going into his last match against Stan Wawrinka on Friday .
Djokovic , 29 , has qualified for the semi-finals after winning his first two group matches at London 's O2 Arena and Murray should also make the last four with two victories going into his last match against Stan Wawrinka on Friday .