Gatlin, 34, stormed to the finish in 9.93 seconds while Ameer followed one-hundredth of a second behind on Thursday. Frenchman Jimmy Vicaut also dipped under the 10 second mark with 9.99, reports Xinhua.
Jamaica's Elaine Thompson posted a season best of 10.87 to take the women's race as American English Gardner came second in 10.92.
Ethiopian Almaz Ayana produced the performance of the day as she ran the second fastest 5000m of all time, clocking 14 minutes 12.59 seconds, narrowly missing out on a new world record.
Ayana's fellow countrywoman Tirunesh Dibaba has kept her world mark of 14:11.15 for eight years.
Two Olympic champions New Zealand's Valerie Adams and Colombia's Caterine Ibarguen, recorded victories in the women's shot put and triple jump respectively.