Top seed Aryna Sabalenka and fourth-seeded Karolina Pliskova set up a tantalising semi-final clash with straight-set wins Friday at the National Bank Open. 

Sabalenka had little trouble with fellow Belarusian Victoria Azarenka in a 6-2 6-4 victory in Montreal, firing seven aces and winning 74.3 per cent of points on her first serve. 

It was Sabalenka's 38th win this season, the most of any WTA player. Another triumph on Saturday would vault world number three Sabalenka past Naomi Osaka and into second in the rankings next week. 

To achieve that, she will have to defeat the only other seeded player remaining in Pliskova as the two stage a rematch of their Wimbledon semi-final won by the Czech.

The world number six downed Sara Sorribes Tormo of Spain 6-4 6-0 to reach the semis for the first time in six trips to the Canadian tournament. 

While Pliskova twice failed to hold her serve in the opening set, she converted all three of her own break point chances before going on to dominate the second set. 

The other semi-final will feature a pair of unseeded players. 

Italy's Camila Giorgi continued her run of upsets in the tournament, knocking out 15th seed Coco Gauff 6-4 7-6 (7-2). 

In the last quarter-final of the day, Jessica Pegula took down 13th seed Ons Jabeur 1-6 7-6 (7-4) 6-0 in a match of wild momentum swings. 

Pegula went the distance for the fourth consecutive match in Montreal, though at one hour, 28 minutes Friday's affair was a full hour shorter than her round of 16 epic with Danielle Collins.