Kenya's Wanyonyi fastest in red-hot 800m heats at Paris Olympics
With none of the Tokyo medal winners in Paris, Wanyonyi still faces a tough field that includes the fastest in the world this year, Algerian Djamel Sedjati, world champion Marco Arop of Canada and French contender Gabriel Tual.
Wanyonyi, Tual and Sedjati all set personal bests under 1:42 last month, with the event's top contenders peaking at the right time.
Days after celebrating his 20th birthday, the Budapest silver medallist Wanyonyi set a quick pace through the first lap and held off Italy's Catalin Tecuceanu (1:44.80) through the second half of the race.
Sedjati is unbeaten this season and he produced a flawless performance to win his heat in 1:45.84.
Running much of the race from the back of the pack, Sedjati made his move heading into the final turn, manoeuvring around the outside to claim the outright lead with 50 metres to go, and he barely looked fatigued as he saluted the crowd at the finish.
The crowd urged on home hope Tual as he held on down the final straight to finish first in his heat in 1:45.13, two-hundredths of a second ahead of Ireland's Mark English.
"We don’t hear us running, we don’t hear us breathing. You have to be in the stadium, in the middle, to believe it. That’s indescribable," Tual said of the crowd's cheering.
"That gives me strength. During the whole race, I wanted to go and run fast. But you have to channel your energy, be patient, wait to keep strength for the finish."
Arop preserved his energy to finish second in 1:45.74 behind Belgian Eliott Crestan (1:45.51) in his heat, after slipping past Australian Peyton Craig (1:45.81) in the last metres.
Britain's world bronze medallist Ben Pattison won the fifth heat in 1:45.56 and Spain's Mohamed Attaoui took the last race of the day in 1:44.81.
The top three finishers in each heat advanced to the semi-final on Friday, while the rest moved on to Thursday's repechage round.