After his gruelling five-set duel with Nikoloz Basilashvili in the intense heat on Friday, the key question was how well would Edmund have been able to recover.
His fatigue was evident but from a set and a break down the 23-year-old ramped up the power on his destructive forehand and romped to a 6-7 (4/7) 7-5 6-2 6-3 victory.
Edmund struck 63 winners, including 25 aces, and his reward is a blockbuster last-eight clash with either third seed Grigor Dimitrov or Nick Kyrgios.
“It’s a good feeling,” said Edmund, who is fast becoming one of the most exciting young talents in the game.
“It was a really interesting match. I didn’t feel I got off to the best start, he was hitting the ball very clean. Once I broke him in the last game of the second set I changed the momentum.”
Edmund was attempting to become the first British man other than Andy Murray to reach the last eight in Melbourne since John Lloyd in 1985, and the first at any slam since Tim Henman 14 years ago.
The rankings made the 23-year-old the favourite - 49 to Seppi’s 76 - while he had won their only previous meeting. But Seppi is a former top-20 player and a man of some pedigree in Melbourne having reached the last 16 on three previous occasions and beaten Roger Federer and Nick Kyrgios twice.
It was clear early in the match that Edmund was not physically fresh. He was allowing balls he would normally have chased down to sail past him and not getting low enough on his groundstrokes.
But the mind was willing and his serve helped him out of a big hole when he faced five break points in the eighth game.
He took a medical time-out for treatment to his right shoulder at 5-6 and held serve to force a tie-break, which was even until Edmund went the wrong way with a forehand and watched despairingly as Seppi landed a backhand winner.
Edmund looked in big trouble when he dropped serve early in the second set but the Yorkshireman responded with a go-for-broke attitude and got his reward with an immediate break back.
It was to prove the turning point. Seppi’s second serve was no match for the Edmund forehand when the 23-year-old unleashed his big weapon at 5-6 and he took his second set point as the Italian’s forehand hit the top of the net and dropped wide.
This was a huge opportunity, too, for the 33-year-old, who was looking to reach his first slam quarter-final at the 52nd time of asking and become the first Italian man through to the last eight here since 1991.
But the sure-footedness with which he had begun the match had started to slip and it was Edmund who suddenly looked full of belief.
He made it five games in a row with another break early in the third set and crunched a forehand winner to repeat the feat and take the set.
Seppi needed treatment to his shoulder during the fourth set but resisted the Edmund pressure well for his first three service games.
However, it seemed a matter of when rather than if the British player would break and so it proved in the eighth game. Edmund pumped his fist and confidently served out his landmark victory.