LUXEMBOURG - Kiki Bertens and Elise Mertens were the lone seeds to advance to the last eight at the BGL BNP Paribas Luxembourg Open out of four in action on Wednesday.
No.2 seed Bertens led Andrea Petkovic by a set and a break, 6-2, 2-1, before the German was forced to retire, while No.5 seed Mertens bounced back from a second set bagel to defeat Madison Brengle, 6-2, 0-6, 6-3.
"I lost against [Andrea] twice this year already," the No.2 seed said. "She's a great player, a great fighter, but I knew from the beginning she was not feeling great. Unfortunately she had to pull out, but I played some good tennis - better than the first match, and I'm happy with that."
Bertens will next face another German in Carina Witthoeft, who advanced with a 6-2, 6-3 win over Russia's Evgeniya Rodina.
"I'm just going to rest a little bit and take care of my body," Bertens said, looking ahead. "I'm jus tgoing to go out there, give all my energy again tomorrow, fight for every point and play as best as I can."
No.3 seed Anett Kontaveit and No.7 seed Beatriz Haddad Maia were not as fortunate, as each were bitten by the upset bug against a resurgent Heather Watson and Bertens' doubles partner Johanna Larsson, respectively.
World No.81 Watson won her first match at WTA level since Wimbledon earlier in the week when she beat Yanina Wickmayer, and surfed that wave of confidence as she took on the Estonian.
Watson’s forehand was impressive throughout, and Kontaveit could find no answer nor defend her serve in the third career meeting between the two players, and second of 2017.
With three breaks of serve, Watson avenged a first-round defeat from the Ladies' Open Biel Bienne in the spring, winning 6-4, 6-4 to set up a meeting with Mertens.
No.7 seed Haddad Maia led Larsson by a set, but was unable to break serve in either of the last two sets, as the Swede used seven aces to rally for a 3-6, 7-6(5), 6-2 victory in two hours, 20 minutes.
After being broken in her first service game of the match, Larsson ran off a string of 13 consecutive holds - only needing to save a pair of break points in the seventh game of the second set.
Four of the last five points in the tiebreak went Larsson's way, as the World No.89 served at 80% in the deciding set and earned a pair of breaks to reach her second straight WTA quarterfinal.
Rounding out the action on the day, qualifier Pauline Parmentier defeated Veronica Cepede Royg, 7-5, 6-1, while Monica Puig edged qualifier Alison van Uytvanck in two tiebreaks, 7-6(2), 7-6(1), to end Wednesday's play.
The most dramatic victory of the day belonged to Watson's compatriot, lucky loser Naomi Broady, who saved match points in the second set to defeat wildcard Sabine Lisicki, returning from injury, 4-6, 7-5, 6-3.