The Scot encountered few difficulties en route to a 6-1, 6-3 success over Isner in Vienna as the big American battled a hand injury during the 74 minutes the pair were out on court.
Murray will face defending champion David Ferrer today, knowing a tournament win in Austria, with a repeat at next week’s Paris Masters would see him reach the peak of the rankings for the first time in his career, as long as incumbent Novak Djokovic does not reach the final in France.
The top seed in Austria was given an early taste of 6ft 10in Isner’s greatest weapon as he delivered two aces from the first pair of points, though the fact he then had to save two break points suggested Murray would be afforded opportunities.
More break-point chances duly arrived and Murray, using the court’s depth to make Isner stoop to uncomfortable positions, claimed them to race to the first set in 27 minutes. It was sealed by an unforced Isner error, his 20th of the set to Murray’s one, and the 31-year-old complained about his grip as he took his seat between games.
The trainer was called for and he taped over a blister on Isner’s right palm, though Murray reeled off the first three games of the second set and was eyeing an early finish.
Isner finally won a game and pumped up the crowd in relief at doing so and he tested Murray’s own serve by going 0-40 up before the Scot dug deep to stave off the threat.
And, having experienced more hurdles in his previous two games, he will have been pleased to progress more routinely this time, with a glorious sliced backhand winner sealing the success.
At the WTA finals in Singapore, defending champion Agnieszka Radwanska booked a last-four meeting with world No 1 Angelique Kerber by ousting Karolina Pliskova in straight sets.
Radwanska and Pliskova knew that whoever emerged victorious in their group-stage clash in Singapore would advance to face Kerber today, and it was the former who triumphed 7-5, 6-3.
Although the Czech broke first in the opening set, the defending champion fought back and took it with a booming forehead return. Pliskova was up a break in the second set too but at 3-2 she lost four straight games to hand Radwanska a semi-final berth.
“I have nothing to lose at the moment; I’m going to play the best player this season,” Radwanska said after the match.
“She [Kerber] has played incredible tennis this year. It’s going to be a great challenge.”