Samaai earned second place with a best attempt of 8.03m, finishing behind London 2017 silver medallist Jarrion Lawson of the US in a competition that only produced three jumps of over eight metres.
Lawson, who finished second behind world champion Luvo Manyonga at the world championships in London, landed the winning jump of 8.19m on his second attempt.
Samaai took an early lead with an opening attempt of 7.94m as one of only three athletes to record a legal jump.
He moved into third place after the second round of jumping, with Lawson moving into first place with his 7.99m while Michel Torneus of Sweden moving into the second spot with 7.98m.
The South African got his hand on the silver medal on his fourth attempt with a jump of 8.03m with America’s Michael Hatfield earning bronze with 8.02m.
Beijing 2008 silver medallist Khotso Mokoena had a terrible start to the competition, inducing two red flags. The former South African record-holder finished last in the field with a best attempt of 7.70m.
South Africa will have three long jumpers in the Diamond League final in Zurich on Thursday, with Manyonga, Samaai, and Mokoena competing for the $50 000 in prize.