Wightman secured Britain’s first victory in the event since Cram in 1983 as he broke with 200 metres remaining in Eugene and held off a field including Olympic champion Jakob Ingebrigtsen.
Cram told the BBC: "What I loved about it was the move with 200m to go. It was brave.
"It was already fast. It would have been very easy to say, I will just sit here and see what I can get in the home straight. No, he said, I will try to win this.
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"That decision with 200m to go is what won it for him, to try to win the race. I couldn't be happier for him."
Wightman crossed the line in a championship record three minutes 29.23 with Ingebrigtsen second and Spain's Mohamed Katir third.
It marked a considerable turnaround for the 28-year-old after he finished 10th at the Olympics in Tokyo last year.
Cram said: "It's just a great story because he is the sort of athlete that so many others can look up to.
"He wasn't smashing records when he was a junior, age-group records or anything. Just steady, steady progress, a real commitment to what he does, believes in himself.
"He is not brash, he just waits until he is ready and he has produced the performance there.
"He is a very smart runner. I don't know too many people who have a better racing brain.
"When he is fit, he puts himself in exactly the right positions."
Ingebrigtsen had led with a lap to go but Nottingham-born Wightman timed his move to perfection to claim the biggest win of his career.
Former British distance runner Paul Radcliffe was impressed with his tactics.
Radcliffe said: "It was stunning the way he ran away (from Ingebrigtsen). They said Jakob was unbeatable.
"Instinct told him he was in the shape to go and he carried it to the line. It was beautiful to watch. He put everything into reaching that line.
"He has a quiet confidence. It is one thing knowing you can win it. It is another thing winning it. He choose his moment and went for it 100 per cent."