Botswana's Amos won silver as an 18-year-old behind Rudisha's world record-setting triumph on the same track in the Olympic final five years ago and although he has been an inconsistent performer since then, he arrived in London in good form on the back of three successive Diamond League victories.
He duly cruised through his heat in one minute 47.10 seconds - more than five seconds slower than his silver-medal winning time in 2012.
Kenya will again expect to be in the medals and their big two had no problems as Emmanuel Korir, fastest in the world this year with 1:43.10 in Monaco three weeks ago, and Kipyegon Bett, the 19-year-old world junior champion advanced comfortably.
Donavan Brazier, 20, looks the brightest hope for an American medal and also qualified well by taking the final heat as the sunny morning was replaced by rain and thunder.
The near-full house created an atmosphere never seen for morning heats - other than at the same stadium in the 2012 Olympics - and athletes of all nationalities praised the fans.
"It was beautiful, I've never seen anything like it. I got to the last 100m and could just hear the roar," said Briton Kyle Langford, who squeezed through as a fast loser.
"As soon as the gun went too you could hear the roar - it was a pretty amazing thing to be honest."
(Editing by Pritha Sarkar)
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