Botswana's Amos won silver as an 18-year-old when David Rudisha set the world record in winning the 2012 Olympic gold on the same track five years ago, but with the injured Kenyan unable to defend his world title in London, Amos should start favourite in Tuesday's final.
If he is to justify that billing, however, he will have to run a tactically more astute race after he had to work hard to claim the second automatic qualifying slot in one minute, 46.29 seconds - the slowest of all eight finalists - behind Poland's 2015 world silver medallist Adam Kszczot.
Canada's Brandon McBride avoided any such problems by front-running his way to victory in the second heat, with Briton Kyle Langford, lifted by deafening home support, climbing from fifth to second over the last 80 metres to go through.
Kenyan Emmanuel Korir, fastest in the world this year with 1:43.10, ran out of steam in that heat to finish third and missed out.
Compatriot Kipyegon Bett, the 19-year-old world junior champion, made no mistake by winning the third heat in 1:45.02, the fastest of the night, chased home by Ethiopia's Mohammed Aman, the 2013 world champion.
Pierre-Ambroise Bosse of France and Brazilian Thiago Andre, third and fourth in the last heat, both went through as the two fastest losers as 20-year-old American champion Donavan Brazier, who had looked so strong in the heats, faded to seventh.
(Editing by Ed Osmond)
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