Sun, who will now face Croatia's Donna Vekic in the quarter-finals, showed ice-cool composure and unflappable bravery to outplay the 2021 US Open champion in front of a pumped-up home crowd on Centre Court.
"It was a great match. I really dug deep to get the win," Sun said in a teary on-court interview.
"I really had to fight tooth and nail because she was obviously going to run for every ball and fight until the end. I don’t even have the words right now."
Raducanu, who had shown glimpses of her best form over the opening week at the All England Club, looked once again a shadow of the player whose stunning triumph as a qualifier at Flushing Meadows nearly three years ago stunned the sport.
From the start, Raducanu seemed off the pace, almost sleepy in comparison to the high-energy Sun, whose ground strokes had far more zip and penetration.
By contrast Raducanu's forehand seemed to lack its usual fizz and she seemed to fear releasing the handbrake, perhaps because every time she did, she was frequently off target.
She seemed unable to build any sustained pressure on the unflappable and indefatigable Sun, whose level rarely dipped below a ferocious intensity.
New Zealand's Sun was superior in all departments racing into a 3-0 lead in the opening set with a double break before comfortably holding off a Raducanu fightback with another break to claim the opener.
The Briton was clinging on for dear life after that, but managed to take the match into a decider with a decisive break in the final game of the second set, yet that was as close as she got to turning the match on its head.
After a nasty fall and some lengthy treatment, Raducanu was broken in the first game of the third set and again as Sun took a 5-2 lead.
Raducanu staved off one match point but Sun would not be denied, smacking a forehand winner to earn another and wrapping up victory when the Briton hit a return long.
