South Africa's Caster Semenya set the year's best time in the 800m at the Diamond League meeting in Eugene as American sprinter Christian Coleman suffered a surprise defeat in the 100m.
Semenya claimed victory in a time of one minute 55.91 seconds.
World indoor 60m record holder Coleman, making his 2018 outdoor debut, finished second to compatriot Ronnie Baker, who won in a wind-assisted 9.78.
Britain's Reece Prescod finished third in 9.88 and CJ Ujah came sixth.
If Prescod's time had been legal it would have been within 0.01 seconds of Linford Christie's long-standing British record.
Marie-Josee Ta Lou won a high-class women's 100m, coming from behind to beat fellow Ivorian Murielle Ahoure in a wind-legal 10.88.
Olympic champion Elaine Thompson of Jamaica took third with 10.98 while British record holder Dina Asher-Smith posted her best 100m time since 2015 to finish sixth in 11:06.
Britain's Laura Muir, who completed her veterinary degree this week, was second in the women's 1500m behind surprise winner Shelby Houlihan from the USA, while team-mate Laura Weightman came 12th.
British world indoor champion Andrew Pozzi battled food poisoning to finish seventh in the 110m hurdles and compatriot Holly Bradshaw came eighth in the pole vault.
There were impressive wins for American pair Noah Lyles (200m) and Shaunae Miller-Uibo (400m).
Lyles stormed away to win in 19.69 and equal South African Clarence Munyai's world-best time for 2018, with Britain's Nethaneel Mitchell-Blake clocking 20.51 for fifth.
Miller-Uibo, the Olympic champion, clocked 49.52 for a comprehensive victory over world champion Phyllis Francis (50.81).