After squandering chances while serving for the match twice in the final set, Murray converted on his fourth match point at the tiebreaker to finally come through. The victory keeps him in position to secure his No. 1 ranking at the end of the season for the first time in his career.
Murray needed 3 hours, 38 minutes to beat Raonic in the longest ever three-setter in the ATP finals.
“Obviously it was unbelievably tough,” Murray said. “I had to fight very, very hard. Being broken twice serving for the match was frustrating. It was one of the harder matches I’ve played indoors. They are never this long. It was really tough.”
Murray may not need to win Sunday’s final to reach his goal.
If Novak Djokovic loses to Kei Nishikori in the second semifinal later Saturday, Murray will automatically guarantee the year-end top ranking. And if Djokovic advances to the final, the winner on Sunday will secure the No. 1 spot.
“I’m tired,” Murray said. “I’ve played so much tennis the last few months. I’ll just give my best effort tomorrow. It’s going to be tough, obviously, but I’ll give my best shot.”
Murray arrived at the tournament simply needing to do better than Djokovic to finish the year at No. 1, a position he has held since winning the Paris Masters this month.
He had won all six of his meetings with Raonic this year, including a straight-sets victory in the Wimbledon final.
Watch ATP Tour Finals live on Tennis Channel