England kicked off their November Nations Championship opener with Borthwick in the spotlight after his side had lost five of their eight previous Tests in 2026.
Senior players such as returning England captain Maro Itoje denied newspaper reports this week of a "toxic environment" caused by Borthwick's management style.
But Jamie George, Ollie Chessum, Joe Heyes and Jack van Poortvliet all crossed Australia's try line before Pollock, best known as a back-row forward, struck twice after replacing injured wing Immanuel Feyi-Waboso at the interval.
Fellow replacement Ben Spencer went over for his first Test try four minutes from time as England piled up their record points tally against Australia, surpassing the 44 they managed in a 44-40 win in Sydney 2016.
Victory enabled England to lay down a marker ahead of a projected quarter-final clash with the Wallabies during next year's Rugby World Cup in Australia.
This was Australia's third loss in a row after they conceded 93 points in total during a pair of heavy defeats by New Zealand last month.
England thought they had made a brilliant start through a Feyi-Waboso try inside two minutes only for the score to be disallowed for a forward pass.
But England only had to wait until the eighth minute for the first try of the match.
Fin Smith, passed fit following a calf problem, kicked a penalty deep and veteran hooker George was driven over from the ensuing line-out.
Smith's conversion from out wide hit the post and Australia reduced England's lead to 5-3 thanks to scrum-half Ryan Lonergan's penalty.
The next score of a scrappy first-half did not arrive until the 26th minute when, after another break by the elusive Feyi-Waboso, the ball was worked across the field.
Recalled full-back George Furbank's floated pass out wide found flanker Chessum, who went in at the left corner.
Smith added the conversion this time and England led 12-3.
Australia were then reduced to 14 men when prop Angus Bell was yellow-carded for a hip-drop tackle on Feyi-Waboso in the 32nd minute.
And England capitalised on their advantage with a third try shortly afterwards when tighthead prop Heyes caught Australia unawares by rolling off the side of a maul.
But the Wallabies hit back on the stroke of half-time with a try from their first meaningful attack.
Max Jorgensen, who scored an 83rd-minute try that sealed a dramatic 42-37 win for the Wallabies at Twickenham two years ago, intercepted Van Poortvliet's pass for a breakaway try.
England fans' favourite Pollock made his presence felt with a strong carry to initiate the move that led to the hosts' fourth try, with Bell still in the sin-bin.
The ball was worked across the field before Furbank's clever inside ball found Tommy Freeman, whose long floated pass then released Van Poortvliet, who went over unopposed.
Then came Pollock's double, the versatile player going over out wide in the 55th minute following a maul before quick hands in midfield sent him in for a second try in barely three minutes.
Australia pulled two tries back through Filipo Daugunu and Jeremy Williams before Spencer had the final say with pretty much his first touch.
England continue their Nations Championship campaign at home to Japan on Saturday, with Australia in action a day later against Scotland at Murrayfield.