After looking likely to make the 31-man squad for his adopted country he suffered an ankle injury that meant he did not make the cut.
However, anyone with a pair of boots and a relative who knew the words to "Bread of Heaven" - and New Zealand-born Anscombe qualifies on both counts - was in with a chance of a call-up as Welsh backs dropped like flies.
Anscombe, having got over the injury that initially made him too risky a selection for Warren Gatland, suddenly found himself called up and thrown straight into the action for his first start against Fiji.
On Saturday he will run out at Twickenham to win his third cap in a World Cup quarter-final against South Africa.
"That first week I was in Dubai sitting in the pool, relaxing, it's certainly been a quick change in a month," Anscombe told reporters after a run out on the Twickenham pitch on Friday (local time).
"When I got the injury in training it was pretty unfortunate. When we looked at my rehab time we thought it would be about a month, maybe enough to get fit for the World Cup. If there were any injuries there would be a chance for me to put my hand up.
"Obviously with the injuries we've had it gave me a chance and now to be here starting a big quarter-final it's a dream come true."
It's probably fair to say that as player who was part of the mighty New Zealand under-20 World Cup side in 2011 and who played Super Rugby as a teenager, the 24-year-old's rugby dreams may have involved a black, rather than red shirt.
However, having moved to Wales two years ago and qualifying to play for them via his Welsh-born mother, he soon came into Gatland's view.
He made his debut as a replacement in the August warm-up against Ireland and his versatility -- he can play flyhalf or fullback -- and goalkicking ability made him a strong contender for the original squad.
Now fully fit and firing, he held off the challenge of the experienced James Hook, who was called up alongside him to replace Scott Williams and Hallam Amos, for the fullback starting berth on Saturday.
"It's a special moment for me, my family are all here, and for the team," he said.
