Coco Gauff battled to a 6-3, 5-7, 6-3 win over unseeded Ukrainian Marta Kostyuk at the Adelaide International 2 WTA tournament on Wednesday to join four other Americans in the quarter finals.
Madison Keys, Alison Riske, Madison Brengle and Lauren Davis also won their respective matches in the round of 16 earlier in the day to book their spots in the quarter-finals which will take place on Thursday.
Gauff, who pushed world No. 1 Ashleigh Barty before losing their second-round meeting in the Adelaide International 1 event last week, raced ahead 4-1 in the opening set against Kostyuk before grabbing the early lead in the match.
Kostyuk raced to 5-3 in the second set and wasted three set points to allow Gauff to draw level, but dragged the clash into a decider when the third seed sent a forehand wide.
A decisive break in the seventh game of the third set gave Gauff the upper hand again and she held her nerve to prevail.Earlier, former US Open runner-up Keys hardly broke sweat in her 6-1, 6-3 straight-set demolition of Czech Tereza Martincova.
Riske was equally ruthless as she powered past Anhelina Kalinina of Ukraine by a similar scoreline. Brengle downed Swede Rebecca Peterson 6-3, 6-2 while Davis was made to work hard by Jasmine Paolini before coming away with a 4-6, 6-4, 6-4 win.
Former French Open runner-up Marketa Vondrousova surrendered a match point against unseeded Croatian Ana Konjuh who completed a 4-6, 6-2, 7-6 (3) victory in an epic Centre Court battle that lasted two hours and 21 minutes.
In the men’s event, Brazilian lucky loser Thiago Monteiro advanced to the quarter finals after top seed Gael Monfils of France retired while 7-6 (2), 3-6, 0-1 down.
Monteiro will play Corentin Moutet in his next match. Tournament organisers said later that Monfils retired due to a neck injury.
Earlier, local hope Thanasi Kokkinakis withstood a barrage that included 23 aces from American John Isner before sealing a 6-7 (5-7), 7-6 (7-5), 7-6 (7-4) victory over the second seed to set up an all-Australian clash with Aleksandar Vukic in the last eight.
 Russian third seed Karen Khachanov saw off Italian Gianluca Mager 7-5, 6-3, while fourth seed Marin Cilic defeated Spain’s Jaume Munar 7-6 (6), 6-2.  Cilic will next face the in-form Tommy Paul, who has won 12 of his past 14 matches, while Khachanov will play France’s Arthur Rinderknech for a place in the semi-finals.
In doubles, veteran Indians Sania Mirza and Rohan Bopanna bowed out after first-round defeats with their respective partners. Sania and Ukrainian Nadiia Kichenok, the second seeds, lost the opening round 3-6, 3-6 to Czech pair of Tereza Martincova and Marketa Vondrousova.
Bopanna and his French partner Edouard Roger-Vasselin lost their first round 4-6, 6-3, 3-10 to Americans Steve Johnson and Austin Krajicek.

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