Making an explosive return to competition, long jumper in the final round, while Montler landed at 8.06m, with the two-time African champion snatching a hard-fought victory.
It was the third Diamond League win of his career.
The fifth of nine legs in the 2020 Diamond League series, which was shortened due to the Covid-19 pandemic, will be held on 2 September in Lausanne, Switzerland.
"Wonderfull performance from Ruswahl," said Aleck Skhosana, the President of Athletics South Africa. "His hard work throughout the lockdown in South Africa has paid off tonight.
"Congratulations to him, his coach and his entire support team for this success especially that while we are still relatively still under an extended lockdown in our country, most of Europe has eased down and their athletes have returned to preparations earlier than us."
- Athletics South Africa