Medvedev was two points away from going out of the tournament but held his nerve in a 2-6, 7-6, 7-6 comeback victory.

The Russian fired 23 aces past his opponent on his way to avenging his defeat to the Pole at Wimbledon in July.

Medvedev will face John Isner in the last four after the American beat Frenchman Gaël Monfils 7-6, 6-4.

Victory for Isner saw him extend his winning streak to nine matches as he booked a place in his first Association of Tennis Professional Masters 1000 semi-final.

Stefanos Tsitsipas of Greece stopped the in-form Norwegian Casper Ruud in his tracks with a 6-1, 6-4 triumph to record a tour-leading 45^th victory of the year.

He is set to play American Reilly Opelka, who dealt an upset to 10^th seed Roberto Bautista Agut of Spain, winning 6-3, 7-6.

At the Women's Tennis Association 1000 event in Montreal, top seed and world number three Aryna Sabalenka swept aside Belarusian compatriot Victoria Azarenka 6-2, 6-4 in just one hour and 19 minutes.

Sabalenka was the aggressor in the match, as she hit 33 winners to Azarenka's eight in a dominant win.

Karolína Plíšková will be waiting for the Belarusian in the semi-finals after the Czech comfortably defeated Sara Sorribes Tormo of Spain 6-4, 6-0.

The fixture will be a rematch of last month's Wimbledon semi-final, which Plíšková won in three sets.

The Czech's return proved crucial as she earned 85 per cent of points on the Spaniard's second serve, helping her to convert six of seven break points on the way to victory.

Italy's Camila Giorgi beat Coco Gauff of the United States 6-4, 7-6 to eliminate yet another seeded opponent.

The world number 71 claimed her semi-final spot after extending her career-best performance in the tournament, where she had previously never reached the round of 16.

Gauff's fellow American, Jessica Pegula, will meet Giorgi in the next round after she staged a superb comeback to overcome number 13 seed Ons Jabeur of Tunisia, 1-6, 7-6, 6-0.