Tunde Ajayi, trainer of light heavyweight contender Anthony Yarde, saw Andy Ruiz pull off a "perfect fight" when he shocked the world last month, when he stopped Anthony Joshua in seven rounds to capture the IBF, IBO, WBA, WBO heavyweight titles.
Ruiz was a huge underdog, who came off the canvas in the third round to score four knockdowns of his own before the contest was waved off.
A rematch is now being worked on, for a date in November or December, after Joshua exercised the option for an immediate return bout.
Ayaji was impressed by the strategy and tactics pulled off by Ruiz.
"It just looked to me that it wasn't his night - but that he could rectify it in the rematch," Ajayi told The James Gray Show.
"But from what I saw and from a technical standpoint, Andy Ruiz Jr fought a perfect fight. He was patient against a guy he knew could punch and had range. Every time AJ jabbed to the stomach, he parried the jab and threw a left hook. Every time AJ jabbed to the head, he parried. This is a guy who knows boxing.
"When Anthony tried to unload on him, he took the punch and came back with a flurry. So this is somebody that has not just done his homework because you don't just prepare for a fight for eight weeks. This is somebody that has been boxing and perfecting his craft for a long time."
At the same time, Ajayi believes the British superstar can do a lot better in the second fight.
"Can AJ do better in the rematch? I think he can because he did drop him but I think that just awoke the lion," Ajayi added.
"Anthony Joshua is someone that I support and that I think has done great for British boxing. He has made the average person on the street pay interest to boxing or to him. He's been great.
"I'd never say everybody can lose - my way is that everybody can win. But AJ came up short that night and let's see if he can bounce back."