England were 13-6 behind early in the second half when full-back Mike Brown, from just in front of his own line, launched a counter-attack that led to a converted try for Red Rose captain Chris Robshaw in the 50th minute.
Seven minutes later, England crossed Australia’s try-line again when fly-half Owen Farrell, who missed three first-half penalties, surprised the tourists by exploiting a gap between Wallaby captain Ben Mowen and hooker Stephen Moore.
The television match official checked for a possible obstruction by England replacement hooker Dylan Hartley on Moore before the try was awarded by Irish referee George Clancy.
England prevented an Australia side who’d posted 33 points, albeit conceding 41 in defeat by world champions New Zealand in Dunedin in October, from scoring at all in the second half.
McKenzie, reflecting on England’s first try, said: “Obviously, it was flashed up on the big screen.
“That was a 90-metre turnaround and there’s seven points at the end of it.
“Theoretically, we should have been having a lineout five metres out (from England’s line).
“The second one (England try) had the benefit of the TMO looking at it without the pressure of the moment.
“We can debate those things until you are blue in the face.
“It’s not going to change the outcome,” former Wallaby prop McKenzie, a member of the Australia side that beat England in the 1991 World Cup final at Twickenham, added.
Australia’s eighth defeat in 11 matches this year, meant their bid to emulate the celebrated 1984 Wallaby Grand Slam — beating England, Scotland, Ireland and Wales on a single tour — didn’t last longer than the first match.
Australia will now look to regroup against Italy in Turin next week.
But for No 8 Mowen, who will hope to beat England at Twickenham when the teams meet in a 2015 World Cup pool match, it was clear the hurt of a ‘blown’ Slam ran deep.
“It’s hugely disappointing. Just after half-time was a real opportunity for us to skip ahead and put pressure on England but we missed a few of those opportunities and they were extremely urgent.
“When you have that urgency, married up with a few things going your way, they created that momentum and took those two tries, so you’ve got to give them that respect.”
Meanwhile McKenzie, who replaced New Zealander Robbie Deans as Australia coach following the British and Irish Lions 2-1 series win over the Wallabies in July, also said he’d no qualms about persisting with his policy of on-field half-time team talks.
At Twickenham on Saturday there was more noise than usual during the break while the England side that beat Australia in the 2003 World Cup final paraded around the field a decade on from their triumph in Sydney.
“There was no problem at all,” said McKenzie.
“We’re fine with that, staying in the moment, staying in the ambience of the game.
“You’ve been going round meeting on the field at half-time for a hundred years.
“I don’t think we have to stress about that too much.”