Kenya's Emmanuel Korir and Pedro Pichardo of Portugal added world titles to their respective Oympic crowns on Saturday, but there was injury heartbreak for Canada's Damian Warner in the decathlon.
Two other gold medallists from last year's Tokyo Games had a mixed bag, Indian Neeraj Chopra having to content himself with silver in the men's javelin, but Dutch runner Sifan Hassan leaving Eugene medal-less after finishing sixth in the women's 5000m.
The 4x100m relays saw the US women beat a loaded Jamaican team featuring individual sprint champions Shelly-Ann Fraser-Pryce and Shericka Jackson, to win gold, but a Canada team anchored by Olympic 200m champion Andre de Grasse beat the favoured US men's team into silver.
Korir produced a trademark kick from 200 metres out to win the men's 800m in 1min 43.71sec, well ahead of Algerian Djamel Sedjati with silver and Canada's Marco Arop bronze.
"I knew there were some guys close behind me in the last 100m," Korir said.
"I was expecting someone to come, but no one did. I never shake my end in training but I do in races. It's like magic. I have been working for this. It's been a long wait -- I failed in 2017 and 2019 and I made it now."
Pichardo was imperious in the triple jump, all but tying up competition when he went out to 17.95 metres on his first attempt.
"I opened strongly," the Cuban-born Pichardo said, adding that he had been mentally focused on the mythical 18-metre mark in a bid to better his two previous silvers.
"My mindset was focused on 18m. It did not come out today, but more importantly, I won gold. This world title was elusive to me."
In the absence of American multiple global medal winner Christian Taylor, world and Olympic bronze medallist Hugues Fabrice Zango of Burkina Faso claimed silver 40cm off Pichardo, while China's Yaming Zhu took bronze.
Warner, also a winner in Tokyo, was in full control of the decathlon after four of the first day's five events, but he pulled up injured a quarter into the 400m.
He was left lying on the track clutching his left hamstring.
Puerto Rico's Ayden Owens-Delermew is now installed as the overnight leader, with the second day of action comprising the 110m hurdles, discus throw, pole vault, javelin throw and 1500m.
- No mercy shown -
Grenada's Peters retained his javelin throw title with a best of 90.54 metres on his sixth and final attempt for victory, having dominated the competition throughout.
"To defend the title is not an easy task. I had to push myself," Peters said.
"The last attempt, I already knew I was a champion but I was working on my technique in every throw and I finally got it through."
Olympic champ Chopra took silver with 88.13m, while Czech Jakub Vadlejch claimed bronze (88.09).
There was also no mercy shown in the women's 5000m, where Ethiopia's Gudaf Tsegay surged down the home straight to win in 14:46.29 ahead of Kenya's Beatrice Chebet and another Ethiopian, Dawit Seyaum.
Olympic champion Hassan could only finish sixth, meaning she will depart Oregon not having made the podium in either the 5,000 or 10,000m.
Hassan produced a stunning 1,500m-10,000m double at the 2019 world championships in Doha before winning 5,000m and 10,000m gold and 1,500m bronze at last year’s Olympics in Tokyo.
But she admitted that she needed seven months out of competition after her exertions, both mental and physical.
"I really overworked last year so I wanted to get a break for my mental part because athletics is not only about running but also about motivation," she said.
"It is so hard to get motivated again."
US track legend Allyson Felix, having deferred her retirement, played her part by helping the US women's 4x400m relay qualify for Sunday's final.
The US team won their heat in 3:23.38, Felix running the second leg, and will be joined in the finl by Britain, Jamaica, Belgium, Canada, Italy, France and Switzerland.
Should the US team medal, Felix stands to win her 20th world medal. Her overall world tally currently stands at 19 medals (13 gold, three silver, three bronze), including four individual golds.