MELBOURNE, Australia – The second week is about to get underway at the Australian Open, and World No.1 Angelique Kerber and French Open champion Garbiñe Muguruza headlining Day 7 Down Under.
We preview all the day’s biggest matchups right here on wtatennis.com.
Sunday, Fourth Round
 Angelique Kerber (GER #1) vs CoCo Vandeweghe (USA #35)
Head-to-head: Kerber leads, 2-0
Key Stat: Vandeweghe is one of four Americans in the Round of 16.
After two tough matches to start her title defense, Kerber looked much stronger in an emphatic third round win over Kristyna Pliskova. The top seed faced down the Czech youngster’s intimidating serve by winning more than half of her points on return as she advanced into the second week for the second straight year.
Her next opponent is into the second week of a major tournament for just the second time in her career, as CoCo Vandeweghe recovered from 4-2 in the final set against Eugenie Bouchard to pull off the win. Vandeweghe hit 11 aces and won 85% of her first serve to topple the former World No.5, and will need a similarly efficient serving day against the defending champion.
Can Kerber keep her hopes of a third Grand Slam title alive?
Sorana Cirstea (ROU #78) vs  Garbiñe Muguruza (ESP #7)
Head-to-head: First meeting
Key Stat: Cirstea is enjoying her best Grand Slam finish since the 2009 French Open.
Muguruza’s first week in Melbourne could well serve as a microcosm of her ups and downs since winning her maiden major title last spring. While the Spaniard hasn’t dropped a set through three wins, she still had a scare halfway through her first round, when she took a medical timeout for fear of exascerbating the right thigh injury that forced her to retire at the Brisbane International.
Despite the hiccup, Muguruza has played her best tennis at a major tournament since last year’s Roland Garros, and will be a tough out for Cirstea, a former World No.21.
The Romanian appeared to be at the height of her career just three years ago when she roared into the Rogers Cup final, but a shoulder injury stunted her progress and led her to re-work her service motion. Winning her first matches in Melbourne since 2014, Cirstea bettered her previous best finish Down Under with wins over Irina Khromacheva, No.10 seed Carla Suárez Navarro, and an in-form Alison Riske.
Can Cirstea cause the first big upset of the second week?
Around the Grounds…
Starting off Day 7 on Rod Laver Arena is an all-Russian affair between No.8 seed Svetlana Kuznetsova and rival No.24 seed Anastasia Pavlyuchenkova, who stunned No.11 seed Elina Svitolina in three sets. No.13 seed Venus Williams follows on Laver against qualifier Mona Barthel.