Lepchenko defeated Mona Barthel of Germany 6-7 6-2 6-3 while Svitolina advanced with a 4-6 7-5 6-1 win over American Alison Riske.
Germany's Kerber came from behind to beat Poland's second seed Agnieszka Radwanska 4-6 6-4 6-4.
Win or lose Pliskova will push herself into the top-10 for the first time when the new rankings are released on Monday.
Only world number one Serena Williams (40-1) has won more matches than Pliskova (38-14) this season.
(Editing by Greg Stutchbury)
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