Unseeded Opelka has now beaten three seeded players, Australian Nick Kyrgios and saved a match point against South Africa's Lloyd Harris on his route to the final.

The world number 32 proved there is much more to his game than just his powerful service as 27 of his 46 winners against Tsitsipas came from groundstrokes.

Opelka's serve was never broken, however, as he triumphed 6-7 (7-2), 7-6 (7-4), 6-4.

Opelka's compatriot John Isner could not replicate his success, however, as he was neutralised by Russian Daniil Medvedev.

The top seed dominated on both serve and return against the American to triumph 6-2, 6-2 after 55 minutes and reach his fifth ATP Masters 1000 final.

Isner is renowned for his big serves and was only broken three times in four matches en route to the last four.

Medvedev countered him perfectly though, breaking his serve four times and winning an unprecedented 50 per cent of his return points.

The Russian impressed from the baseline by smashing 11 aces, including four consecutive ones to close out the first set in emphatic fashion.

The combination of his impenetrable return and stunning serving put pressure on Isner to play more aggressively when he was able to work his way into points, leading to unforced errors.

The world number two has already lifted trophies this year in Marseille and Marbella as he looks to avenge his 2019 loss to Spaniard Rafael Nadal in the final of this event.

Meanwhile in Montreal, Karolína Plíšková of the Czech Republic is into her third Women's Tennis Association (WTA) singles final of the season.

Fans were expecting to be at the IGA Stadium for the long haul as the world number six came up against top seed Belarusian Aryna Sabalenka.

However, the Czech eased past her opponent in straight sets - 6-3, 6-4 - to even out the pair's head-to-head record at two wins apiece.

Plíšková battled back from a break down in the second set to clinch the victory after an hour and 21 minutes of play.

Overall, it was a composed display by Plíšková, who converted four of her eight break points and collected two thirds of points returning Sabalenka's second serve.

In the other semi-final, Italy's Camila Giorgi extended her giant-killing run all the way to the final, defeating American Jessica Pegula 6-3, 3-6, 6-1, to reach the first WTA 1000 final of her career.

World number 71 Giorgi, who beat top-25 players Elise Mertens of Belgium, Czech Petra Kvitová, and Coco Gauff of the United States en route to the semi-finals, added another upset to the list this week by taking down world number 30 Pegula in a hard-fought match lasting more than two hours.

Giorgi and Plíšková have met in a final once before, with the Czech taking the win in 2014 in Austrian venue Linz.