Murray, who won all three of his group play matches, moved into the semis by taking out Stan Wawrinka in straights on Friday. Murray made no mistake when coming to serve for the match, with a shanked Wawrinka forehand to sending the Wimbledon and Olympic marching into the weekend.
Both Murray and the Japanese player (1-1) are bound to be jaded Friday when they respectively face Stan Wawrinka (1-1) and Marin Cilic (0-2), US Open champions present and past. In previous years, he might well have faltered but the confidence from winning so many matches has unquestionably helped him at such moments.
"It's very big for me", said Raonic. The last time an alternate won a match at the Tour Finals, Djokovic was on the other side of the net, beaten 3-6, 7-5, 6-1 by countryman Janko Tipsarevic and eliminated from the tournament. "Numerous players have been talking about this format and the schedule, top players especially, because it just comes right after Grand Slams, right after World Tour Finals".
"I guess you play more matches", said Djokovic, who won a bronze medal at the 2008 Beijing Games. "It's normally the next day when you feel stiff and sore, but there's hopefully three days left in the season, and I'll give my best to get through as many matches as I can".
Raonic, 25, had just one more Finals appearance on his résumé than the first-time Thiem, 23.
Murray will next face Milos Raonic of Thornhill, Ont., on Saturday, while Djokovic meets Kei Nishikori.
As befits the way in which his game fell away sharply especially in second set, a forehand shank sent Murray to the top of the group with a flawless record in the round robin for the first time, and into the semi-finals for the third time. "But, yeah, I feel like my game's in a good place".
"Of course, they have to change", he said.
The set ensured Murray of progress to the next stage, but he wanted top spot to avoid Djokovic next and duly set about putting a visibly deflated Wawrinka to the sword.
Do you know: If Murray fails to qualify for the semi-finals of the ATP World Tour Finals 2016, Djokovic will finish 2016 as the World No. 1.
LONDON (AP) - Novak Djokovic is a fan of the round-robin format in tennis, and he would even like to see it used at the Olympics and the Davis Cup.
Murray said: "I weathered the early storm a little bit".
Whichever player-Murray or Djokovic-fares better from this point forward will finish the season atop the rankings.
He saved break points in the third, fifth and 11th games, aimed verbal volleys at coach Ivan Lendl and at one point the wedding ring he ties to a lace of his military style black shoes broke loose and threatened to roll away. "When he plays his best tennis, he's unplayable".
"For a lot of the players, we would play it regardless of whether there's points or not". I played really good today and it was a pleasure to get a good performance at the end of the week.
Nishikori showed commendable resolve to retrieve one break, but Murray served out at the second time of asking.
Murray knew he only needed to take one set to be certain of reaching the last four, but he had to win the match to be assured of topping the group.