Halfpenny's unerring accuracy has been a key feature of this Lions tour but after missing his first kick - which struck the crossbar - in Melbourne, he fell short with his late, long-range effort from more than 50 metres.
But Lydiate, who left RaboDirect PRO12 side Newport Gwent Dragons at the end of last season, is convinced that Halfpenny would hit the target if he found himself in the same situation again.
"It's just one of those things and I'm sure the next time he's in that position he'll slot it," said Lydiate.
"I'd back him every time. Watching that guy train, he trains like a demon and is always doing his extras.
"That's the thing with Leigh, he's a perfectionist and unless he kicks 100 per cent then he's never happy.
"Everyone is going to miss a kick every now and again and [Saturday] was the day. No-one is blaming him for missing that kick - it's awesome to have him in the team.
"If we get a penalty that far out, the bet's on that he's probably going to slot it over, which is brilliant for us."
Cardiff Blues flanker and Lions captain Sam Warburton has been ruled out of the decider in Sydney with a hamstring injury.
He said: "It is incredibly disappointing to be ruled out of the tour through injury as we head to Sydney for the deciding match.
"I wish the team all the best and hope I can play some part in the build up this week. I am confident that the boys can finish the job off and secure the series win."
63x46.png){kind=logo}