Kazakhstan's Elena Rybakina advanced to the National Bank Open semifinals after Ukraine's Marta Kostyuk was forced to retire with an apparent arm injury while trailing 6-1, 2-1 in women's singles action Monday in Montreal.

Rybakina, the ninth seed, converted three of her 10 breakpoint chances in the quarterfinal matchup at IGA Stadium. The players shook hands at the 54-minute mark before the 24th-seeded Kostyuk exited the court in tears.

After the third game, Kostyuk's trainers wrapped her forearm in medical tape.

Rybakina will face the winner of Monday night's matchup between Canadian teen sensation Victoria Mboko and Jessica Bouzas Maneiro of Spain.

Mboko upset top-seeded Coco Gauff of the United States in straight sets Saturday, winning the lopsided match in just 62 minutes.

WATCH | Toronto teen Mboko upsets tournament No. 1 Gauff: 

Canada's Victoria Mboko upsets No. 1 seed Coco Gauff at National Bank Open

The Canadian tennis star beat Coco Gauff in straight sets to reach the National Bank Open quarters.

The 18-year-old from Toronto has surged from outside the top 300 to No. 85 in the world rankings in a breakthrough year.

The National Bank Open — a WTA 1000-level event — runs through the final on Thursday. The tournament's top-five seeds were eliminated before the quarterfinals.