His made it a double barely six minutes later, grabbing a Paul Vaughan offload and turning Knights fullback Kurt Gidley inside out with a superb left-foot step.
He brought up the hat-trick in the 15th minute after winning the race to a clever kick in-goal.
"Every time I see him play I'm more impressed with him," rugby league immortal Andrew Johns said during commentary for the Nine Network.
"What a player."
Jarrod Croker scored Canberra's fourth try and then converted in the 23rd minute to overtake Mal Meninga as the Raiders' third-highest tryscorer of all time.
Newcastle hit back with one of their own on the half-hour mark to enter the break 24-4 down.
With the return of Tyrone Roberts and playmaker Jarrod Mullen together for the first time since Anzac Day, the Knights had hoped their first-choice halves pairing would spark their attack in Canberra.
But Mullen - back after 10 weeks on the sidelines with a foot injury - appeared a shadow of himself, hobbling at times.
Dane Gagai also struggled, having made his Origin debut barely 48 hours earlier in Queensland's series-winning victory in Brisbane.
But his Maroons teammate Papalii showed no signs of fatigue, adding to his maiden Origin try with a double both scored in the first 10 minutes of the second half.
Akuila Uate answered with a pair of tries and Kane Snowden a four-pointer of his own, but it was too little too late for the Knights.
The night, however, ended on a sour note for the Raiders, with in-form halfback Sam Williams taken off late in the second half with a suspected pectoral injury.
Coach Ricky Stuart lauded Austin's effort, but was particularly proud of Canberra's defence given they only had 40 per cent of possession.
"We didn't have any ball in their end and still we scored some good tries," Stuart said.
"But defending our goal-line was probably the strong point for us."
Stuart believed Austin - who's scored 11 tries in the past nine games - still had room to grow.
"Blake will keep improving as the little things in his game does," the Raiders mentor said.
"We all know he can attack, and he was wonderful in that area tonight."
Rick Stone said the Knights weren't "even close" to NRL standard in the first 20 minutes and failed to keep up with Canberra's speed.
"Having our halves back definitely helped, but even the world's best halves aren't going to win you games if your defence isn't good enough at the start of the game," Stone said.
"The signs before the game were good, but it was like we got off the bus and forgot we had to work together defensively.
"We were playing like under-8s and making individual tackles ... and it showed on the scoreboard."
- AAP
