The former coach of Dan Evans, who knocked the 11th seed out of the US Open, said it was clear from an early age that the British player had a natural ability.
The 23-year-old, who is ranked 179th in the world, clinched a 6-4 6-4 6-2 victory against Kei Nishikori in New York.
Scott Key told ITV News: "I think this a big opportunity for him to take on this as a big move forward in his career. Undoubtedly we all knew he had the talent but I think it's actually having the belief in his own talent and that's what's changing."
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After a cold start, it will be a mostly bright and sunny Sunday for many of us with temperatures way above the norm for the time of year.
In a wide-ranging Peston on Sunday interview, he said Parliament security needs reviewing and the PM's counter-terror strategy is flawed.
The star celebrated his 70th birthday with his family before attending a celebrity-filled bash held in his honour.