Murray had a degree of freshness having seen his quarter-final end prematurely with David Goffin needing to retire injured, having lost the first set 6-2.
And in what was his first ATP Tour-level semi-final in 822 days, Murray showed all the class in his returning game against one of the Tour’s biggest servers in 6ft 11in Opelka to win it 6-7, 6-4, 6-4.
Roared on by plenty of noisy Scots inside the Ken Rosewall Arena, the former world No 1, who has reached only his second final since injuries started to take their toll in 2017, showed he remains a force on the ATP Tour despite his physical ailments and this was another stunning display that tees him up for the Australian Open.
Victory in the final, where he will face tournament top seed Aslan Karatsev, would see Murray restored to the top 100, too.
Andy Murray has reached his first ATP Tour-level final since October 2019 after his latest win
It was an excruciating watch as an emotional Murray slugged it out at the Sydney Classic
He came up against big-serving 6ft 11in Reilly Opelka but Murray showed his class returning
Murray looked to be exploring Opelka’s bullet serves on the fly in an opening set that looked destined to be settled via a tiebreak from the moment it began.
The Scot did well in keeping the ball in play but soon lost his stranglehold in the tiebreak when he fell to an early 3-0 deficit.
A late rally back put some doubt in Opelka’s mind but the American, who is targeting a return to the world’s top 20 this month, held well to take the opener 7-6.
‘I love competing,’ Murray said.
‘You want to finish matches quickly. I obviously lost a tight first set and it’s not easy to come back against someone who plays that play style but I kept fighting.’
Using a blocking tactic, Murray was able to neutralise the big serves more often than not
Opelka dug in and took the opening set as he punished Murray’s decision-making in a tiebreak
ANDY MURRAY’S ROUTE TO THE FINAL
L32: d. Viktor Durasovic (6-3, 6-1)
L16: d. Nikoloz Basilashvili (6-7, 7-6, 6-3)
QF: d. David Goffin (6-2, retired)
SF: d. Reilly Opelka (6-7, 6-4, 6-4)
Murray was vocal throughout this one while Opelka, who can be quite outspoken, was something of a mute on the other side of the net.
An early break in the second set felt – and later proved – decisive for Murray and he soon upped the tempo on his service games to rattle through points, not allowing Opelka to settle and find his rhythm.
At one set apiece it was a straight shootout for the first spot in Saturday’s final and it proved almost as nip-and-tuck as the opener.
The pendulum of momentum looked to be swinging to Murray at 3-3 with Opelka serving.
Murray thought he had figured out Opelka’s serve at this point and with two break points at 15-40 he sensed an opportunity to take control.
A 141mph serve was quickly fired in his direction by Opelka, who went on to hold following some unforced errors courtesy of Murray.
‘Why did I change direction?’ Murray shouted aloud. ‘Rushing, rushing. Absolute madness.’
Murray held in a much more straightforward manner and it was at 4-4 where he finally broke Opelka’s resistance.
Opelka’s improvisation saw him attempt a ‘tweener’ but he soon lost his early set advantage
Down 15-30, Opelka panicked and looked to close the distance as he raced to the net.
Murray perfectly pulled off a passing shot down Opelka’s forehand to set up two break points, which he converted in the following point.
A huge roar followed and Murray was able to to serve for a spot in the final and then, after two hours and 24 minutes, celebrate his latest scalp as he takes a step closer to his 47th career title.
Asked about dealing with Opelka’s serve, Murray conceded he was improvising throughout.
‘You can’t prepare for it to be honest,’ he said. ‘I chose to block quite a few which worked quite well and the second serve isn’t easy.
Murray refused to wilt and he converted breaks in sets two and three to reach Saturday’s final
‘It’s tough but return has been always one of the strongest parts of my game and I used it well today.’
On the prospect of a 47th career title, he added: ‘It would be amazing to start the year with a win, really big progress to string matches together.
‘I’ll go for 47 tomorrow and it’s been a good week. I’ve played better in each match.’
He has the prospect of facing Dan Evans, who is in semi-final action against Aslan Karatsev later in the session.
An all-British final at ATP Tour level has never happened and so it would be history made if Evans progresses.