Olympic 800m champion David Rudisha was seventh on his return from injury at the Diamond League meeting in Eugene.
The Kenyan, who broke the world record at London 2012, missed last year's World Championships with a knee injury and has had a calf problem this season.
His time of one minute 44.87 seconds was more than a second slower than that of winner Nijel Amos (1:43.63), with Briton Andrew Osagie eighth.
In the 100m, American Justin Gatlin ran 9.76 seconds to beat Michael Rodgers.
Frenchman Jimmy Vicaut was third, with Jamaica's two-time Olympic gold-medallist Nesta Carter fourth.
In a thrilling finish to the 400m, Grenada's Kirani James pipped Lashawn Merritt with both men clocking 43.97 seconds, while Britain's Martyn Rooney was sixth.
Elsewhere, Briton Shara Proctor (6.60m) finished sixth in a long jump competition won by Serbian Ivana Spanovic, who claimed victory on count-back from Russian Darya Klishina after both jumped 6.88m.
Proctor's compatriot Eilish McColgan was 11th in the 3,000m steeplechase, her 10:15.59 more than a minute slower than winner Sofia Assefa, whose 9:11.39 is the best of the year so far and a meeting record.
American Will Claye also broke the meeting record, his 17.66m in the triple jump four centimetres better than the mark set by countryman Christian Taylor, who finished second.
Kenya's Hellen Obiri beat world champion Abeba Aregawi into second place in the 1500m, her time of 3:58.58 another meeting record, with Britons Laura Weightman and Hannah England eighth and 11th respectively.
American long-jumper Tori Bowie recorded the fastest time in the world this year to win the 200m in 22.18 seconds, with two-time Olympic gold-medallist Shelly-Ann Fraser-Pryce last.
On Friday, Mo Farah's training partner Galen Rupp won the 10,000m in 26:44.36, breaking his own US national record and finishing almost five seconds clear of Paul Kipngetich Tanui.