Thomas Roehler stunned the crowd with the second-best javelin throw of all time, 93.90 metres, and Elaine Thompson won the latest round in her rivalry with Dafne Schippers in the women's 200 metres.
Simbine, fifth in the Olympic final last year, defied a strong headwind and managed to dip under the 10 second barrier, clocking 9.99 seconds as he left his better-known rivals in his wake.
Jamaican Powell was second in 10.08 while Olympic silver medalist Gatlin was fourth and Olympic bronze medalist Andre de Grasse of Canada fifth.
Germany's Roehler was as surprised as anyone by his effort to win the javelin.
"I did not see that coming, I did not expect that in the first start of the season," he said. "I'm second best, ever. It will take some days to realize that."
Nevertheless, he was still some way behind the world record of 98.48 set by triple Olympic champion Jan Zelezny.
Fellow German Johannes Vetter was also impressive, finishing second with 89.68.
Thompson and Schippers provided another rematch of the last two major championships as they met again in the women's 200 metres.
The Jamaican led off the bend and broke further away down the final straight to win in 22.19.
Schippers won at the world championships in 2015 with Thompson second, while the positions were reversed at the Rio Olympics.
"It was a tough race, maybe it was the wind. The time was good, and that's OK for now," said Schippers.
Olympic champion Caster Semenya of South Africa easily won the women's 800 metres in one minute 56.61 ahead of Kenya's Margaret Wambui.
Ruth Jebet, the Olympic women's steeplechase champion, finished in third as her race was won by Kenya's Hyvin Kiyeng in 9:00.12
Steven Gardiner of Bahamas easily won the men's 400 meters in 44.60 seconds ahead of Olympic bronze medalist LaShawn Merritt who was not happy with his own performance.
"It's a little windy. It's the start of the season so I feel good, but should of done better so looking forward to the rest of the season," said the American.
Elijah Manangoi led going into the last lap and held off a challenge from fellow Kenyans Silas Kiplagat and Bethwell Birgen to win the men's 1500 meters in 3:31.90.
(Writing by Brian Homewood, editing by Pritha Sarkar)
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