Agnieszka Radwanska
Agnieszka Radwanska reached the Australian Open semi-finals in 2014 and 2016 SAEED KHAN/AFP/Getty Images

Agnieszka Radwanska became the latest high-profile casualty of the Australian Open on Thursday (19 January). The third seed, a two-time Melbourne semi-finalist, followed in the footsteps of Novak Djokovic by exiting the tournament in the second round after a shock 6-3, 6-2 defeat to 79th-ranked Croatian veteran Mirjana Lucic-Baroni.

"It's amazing, it's been so long since I won a match or two ... actually this is the first time ever in Australia," Lucic-Baroni, who will now face Maria Sakkari after the latter knocked out Alize Cornet in three sets, said after completing a remarkable upset. "I knew until the last point that I had to fight – there is a reason why she is number three in the world.

"I know I have a big, strong game and that I can hurt a lot of people. Whether I can do it seven days in a row is a question. But I know I have a big enough game to beat anybody. I knew what I had to do. It's just a matter of getting on court and doing it and I was able to execute perfectly tonight. I'm super thrilled."

Defending women's champion Serena Williams avoided a similar fate, following up her opening victory over Belinda Bencic with a comfortable 6-3, 6-4 triumph against Lucie Safarova. Fellow American Nicole Gibbs, conqueror of 28th seed Timea Babos in round one, is up next as the six-time Australian Open winner seeks to move clear of Steffi Graf and claim an Open era record 23rd career Grand Slam singles title.

In a one-sided late-night affair at Rod Laver Arena, Rafael Nadal faced little resistance as he swatted aside Marcos Baghdatis in emphatic fashion 6-3, 6-1, 6-3. Alexander Zverev now lies in wait.

Serena Williams
Williams celebrates her win over world number 61 Lucie Safarova Clive Brunskill/Getty Images

Elsewhere on day four, world number three Milos Raonic hit 21 aces en route to dispatching Gilles Muller and booking a third-round tie against Gilles Simon. Dominic Thiem, Gael Monfils, David Goffin, Roberto Bautista Agut, Grigor Dimitrov, Richard Gasquet, David Ferrer and Ivo Karlovic all progressed alongside Philipp Kohlschreiber.

Karolina Pliskova and Dominika Cibulkova remain in the running, as do Elena Vesnina, Barbora Strycova, Timea Bacsinszky, Caroline Garcia, Ekaterina Makarova and Yulina Putintseva. Former WTA Tour number one Caroline Wozniacki easily defeated Donna Vekic and adopted Australian Daria Gavrilova overcame a second-set wobble to eliminate Ana Konjuh.