In the men's high jump, Ukrainian Andriy Protsenko won with a leap of 2.27 metres.
A strong finish from Canada's Olympic 200m silver medallist Andre de Grasse earned him victory in a meeting record of 20.03 after he had overhauled the American Trials victor, Ameer Webb, who finished second in 20.18 in front of Britain's Zharnel Hughes.
Although World Junior 800m champion Kipyegon Bett has already qualified for the finals, the meeting could be an ultimate final rehearsal if the standings remain the same until the last leg.
Another home hope, 21-year-old Soufiane El Bakkali, saw off Kenyan rival Jairus Kipchoge Birech in the men's 3000m steeplechase in a personal best of 8min 05.12sec, and compatriot Abdelaati Iguider won the men's 3000m.
Miller Uib coasted home in 49.80, but Semenya was well back in seventh in a time of 51.53, though that was her best run of the Diamond League series.
The Rio Olympic champion eased to a second victory of the season and set another meeting record with a 49.80 seconds, finishing nearly a second before runner-up Natasha Hastings of the USA.
In a race billed as the battle of the Olympic champions, 400m medalist in Rio de Janeiro a year ago Shaunae Miller-Uibo once again showed why she is the athlete to beat in the single lap event, running a blistering time of 49.80s, more than a second ahead of Americans Natasha Hastings (50.86) and Quenera Hayes (51.08).
Toronto's Shawn Barber, who won his event at the nationals, finished fourth in the pole vault competition as he cleared 5.60m.
American Ryan Crouser claimed a 10th straight win in the shot put with 22.47 metres, while Colombia's Olympic champion Caterine Ibarguen returned to winning ways in the triple jump with 14.51 metres to beat Jamaican Kimberly Williams (14.31m) after defeat by Yulimar Rojas in Rome. I hold the meeting record and I wanted to improve that today.
Samaai won the men's long jump after an early ding-dong battle with American Jarrion Lawson.
Canadian sprinter Andre De Grasse finished first and set a meeting record in the 200-metre race at the Diamond League stop in Rabat, Morocco, on Sunday.
Ben Youssef Meite of Cote d'Ivoire was second in 10.01, with Britain's Nethaneel Mitchell-Blake third in 10.18. Nijel Amos of Botswana won the gold with 1:43.91.