The world's sixth-ranked bowler got through a decent workout at the Adelaide Oval nets late yesterday afternoon to give his back a solid test.
Boult has been troubled by an irritated disc since the first test in Brisbane earlier this month.
He's taken six wickets in the two tests so far, but has been below his best.
Yesterday the left arm swing bowler got through eight overs in two spells, five of which were at full intensity. There were no signs of caution in his movements.
Now it's all down to tomorrow, and whether Boult wakes with no problems and gets through another spell in the nets.
"Today was never a definitive day. Today was just the next step," New Zealand coach Mike Hesson said last night.
"He got through today, that's what we wanted him to do, so we just have to see how he scrubs up tomorrow. But he got better as the day went on."
Hesson saw nothing to be alarmed about; plenty to have him cheerful, pronouncing himself "relatively confident".
He also confirmed the balance of New Zealand's team won't change from the drawn second test in Perth.
That is, wicketkeeper BJ Watling will bat at No 6 - and he's had a lean time with the bat in the series - with four seamers and spinner Mark Craig.
It means if Boult's progress goes awry today, it's almost certain fellow left armer Neil Wagner would come in to make a like-for-like change.
There had been consideration given to playing two spinners, with left armer Mitchell Santner as Craig's sidekick. But that won't happen, and especially having seen the grass cover on the strip.
New Zealand had a two and a half hour training session yesterday, with special lights brought in for the nets kicking in shortly before they finished.
They have a fielding session under lights on the oval tonight.
Hesson likes the look of the grassy Adelaide pitch, likening it to a New Zealand wicket - "more grass than we've had in the last week but a bit less than the Basin Reserve. It looks a good surface".
Australia's final XI also looked to be taking shape yesterday.
Left arm spinner Steve O'Keefe is expected to sit the test and the likelihood is that after three days of James Pattinson's recall to the side being predicted by Australian media, seamer Josh Hazlewood will retain his place.
Part of that thinking is Australia are loathe to make too many changes at once. Already they've lost batsman Usman Khawaja to injury (replaced by Shaun Marsh) and the retired Mitchell Johnson, whose place is expected to go to veteran seamer Peter Siddle.
Two forced changes is enough, goes the thinking.
As they left the oval last night they passed the arriving Australians. They get on well enough.
But handshakes? Slams on backs as they passed? Piles of bonhomie? Yeah right. There's serious business around the corner.
- By David Leggat of the New Zealand Herald, in Adelaide
