Coco Gauff in action against over unseeded Ukrainian Marta Kostyuk at the Adelaide International 2 WTA tournament on Wednesday. ADELAIDE: 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 number one Ash 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 U.S. Open runner-up Keys hardly broke sweat in her 6-1 6-3 demolition of Czech Tereza Martincova while 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) 7-6(5) 7-6(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.