Friday night's friendly had been billed as Kerr's first game on home soil for two years -- but the captain remained on the bench with a calf complaint after also missing Chelsea's last two games.
Kerr only returned from her ACL injury in September and carried the calf issue into Matildas camp but she's expected to face New Zealand in Adelaide next week.
"She's just had a grumbly sort of calf, it hasn't settled properly," Montemurro said.
"We just decided with Sam and the medical staff and the technical staff to just give her a little bit more time and get her ready for Tuesday."
Without their star forward, Australia flexed considerable attacking muscle on the Kiwis in their penultimate game before next year's home Asian Cup.
Katrina Gorry was a menace going forward for the Matildas, who confirmed a big win with two goals in a two-minute blitz during the second half.
Gorry's high work rate was rewarded with a goal in second-half added time after Holly McNamara cut back from the left side of the box.
The victory is the Matildas' most convincing from seven games under Montemurro, eclipsing a 3-0 win over Slovenia.
Montemurro could still see room for improvement.
"They hurt us a bit with their wing backs very, very high and a couple of times we got exposed," Montemurro said.
"But all in all, we wanted to go out and control the game, we wanted to make sure that we dictated when we decided to go forward, and rotate to prepare opportunities to go forward, and we found some space by being patient."
The Football Ferns, 33rd in the FIFA rankings, made little impact in the final third and came up with some diabolical defensive errors on which their hosts pounced.
"They were the side I thought they'd be, good in transition, good quality all over the park," said New Zealand coach Michael Mayne.
"Disappointed, obviously, there's nothing nice about that scoreline but I'd say three of those goals we were well responsible for."
On the hunt for a new club in 2026, Amy Sayer opened the scoring after 12 minutes thanks to a slick pass from Gorry, who'd broken forward into space.
The 23-year-old Sayer could've had a second goal in the first half but struck the woodwork.
It was instead speedy winger Hayley Raso who doubled the Matildas' lead following a mistake at the back from the Football Ferns.
Maya Hahn tried a one-two with Michaela Foster, only to have her pass picked off by Raso, who caught goalkeeper Anna Leat out of place as she curled the ball home.
After a better start to the second half, the Kiwis were left to rue another defensive lapse as Liz Anton kicked straight to Ellie Carpenter coming out of trouble.
Carpenter made no mistake scoring a fifth Matildas goal, before Kyra Cooney-Cross netted with a spectacular shot from 30 yards only seconds after play resumed.
The Matildas could've had a sixth in the final minutes but Steph Catley thundered a penalty into Leat, who'd taken McNamara out just after Gorry's goal.
Montemurro had flagged his concerns about the Football Ferns' high press in the lead-up but the visitors took until the 58th minute to register a shot on target.
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