Madison Keys' Coupe Banque Nationale title chances have improved without her hitting a ball, as seeds fell in the top half of the draw in Quebec City.
Keys, ranked 18th, is red-hot favourite to win the WTA International event, given world number 53 Lucie Hradecka is the highest-ranked player left to challenge.
In top seed Keys' half of the draw, sixth seed Tatjana Maria and eighth seed An-Sophie Mestach were both ousted on Tuesday - a day after third seed Mona Barthel bowed out.
Germany's Maria was ousted by Alexa Glatch, the American prevailing 1-6 6-4 6-1, while Mestach fell to Poland's Paula Kania 6-4 6-3.
One of Kania (ranked 150th), Jessica Pegula (177th), Jelena Ostapenko (101st) or Sesil Karatantcheva (110th) will reach the semi-finals.
Qualifier Pegula came from a set and 5-2 down to upset Nicole Gibbs 1-6 7-6 (7-2) 7-6 (7-4).
The bottom half of the draw saw all seeds through to the second round at the event played on carpet, with second seed Mirjana Lucic-Baroni among them.
Lucic-Baroni, whose ranking plummeted 56 spots in one week to 104th after losing her US Open fourth-round points from 2014, moved into the second round when wildcard Francoise Abanda retired.
Lucic-Baroni was leading 6-3 3-1 when Abanda withdrew with an apparent neck injury.
Fourth seed Hradecka downed Donna Vekic 6-2 6-4, while seventh seed Evgeniya Rodina was too good for Sachia Vickery 6-2 6-2.
Joining Pegula in the second round were fellow qualifiers Samantha Crawford and Amandine Hesse.
Crawford thrashed another qualifier Mandy Minella 6-2 6-1, while Hesse - of France - surpassed Maria Irigoyen 6-3 6-2.
Keys will get her tournament underway on Wednesday, when she meets fellow American Anna Tatishvili in the first round.