Day four of the Australian Open saw the heat on the court prove to be a stumbling block for many competitors at Melbourne Park. The tricky conditions proved to be an issue for some seeded players who made hard work of progressing to the third round. As ever, we round up the key moments from today’s action. 

Six-time Australian Open winner Novak Djokovic battled the searing heat to progress to the third round, defeating 2018 Qatar ExxonMobil winner Gael Monfils 4-6 6-3 6-1 6-3.  After a promising start, Monfils lost his way on Rod Laver Arena as temperatures neared 40 degrees Celsius in Melbourne. The talented yet underachieving 31-year-old was unable to settle after beginning to seriously struggle midway through the second set, eventually falling in two hours, 45 minutes to the 12-time grand slam champion.

Fifth seed Dominic Thiem came from two sets down to get the better of Denis Kudla to book his place in the next round. The Austrian has been widely seen as a credible challenger to break the dominance of the ‘big 4’ however the 24-year-old founding himself a set down, and broken by American Kudla in the second set. However, Thiem fought back in impressive style to take the match 6-7 (6-8) 3-6 6-2 6-2 6-3. A match against Czech Jiri Vesely or  France's Adrian Mannarino awaits. 

Former US Open champion Juan Martin Del Potro fought off rising Russian star Karen Khachanov as he battled through the pain barrier to reach the third round. The Argentine 12th seed needed 3hr 45 min in oppressive court conditions to see off the 47th-ranked youngster 6-4, 7-6 (7/4), 6-7 (0/7), 6-4 on Hisense Arena.

Del Potro, in his first appearance in Melbourne for four years after wrist injuries, will face Czech veteran Tomas Berdych in the third round.
Del Potro, who reached the third round in Melbourne for the fifth time, is looking to improve in his quarter-final appearances in 2009 and 2012, losing to Roger Federer both times.

Over in the women’s draw, and third seed Garbine Muguruza was the latest big name exit from the Australian Open as the Spaniard crashed out at the hands of Hsieh Su-Wei from Taiwan.  With temperatures rising on Rod Laver Arena, Muguruza struggled to get started finding herself 5-2 down in the first set. The Spaniard came back to force the tiebreak, however eventually losing 7-1. 

It was also the same case in the second set, with Muguruza finding herself 5-2 down. The two-time Grand Slam champion attempted a comeback, breaking Su-Wei’s serve and saving a match point. However, the Taiwanese player who is ranked 88 in the world wasn’t to be denied and served out the match eventually winning 6-4. Su-Wei will now take on Agnieszka Radwanska of Poland in the next round. 

Top seed Simona Halep marched into the third round of the Australian Open with a straight-sets victory over Eugenie Bouchard. Halep was troubled by an ankle injury in her first-round match against Destanee Aiava, but was moving freely on Margaret Court Arena as she wrapped up a 6-2 6-2 victory. 

The 112-ranked Bouchard held serve only once and made 23 unforced errors, Halep capitalising to set up a meeting with Lauren Davis. Halep, eyeing an elusive first grand-slam success, was broken twice in her first three service games of a strange first set but was too good for the former world number five.

British number one Johanna Konta fell to a shock second-round loss at the Australian Open as lucky loser Bernarda Pera's dream run continued in Melbourne. Pera stunned the ninth seed 6-4 7-5 in a huge upset on Thursday.  The 23-year-old Pera lost in qualifying and only made it into the main draw of a Slam for the first time as a lucky loser after another player withdrew through injury. The American will now progress to the third round to take on 20th seed Barbora Strycova. 

Men's Singles 

2nd round

Albert Ramos (ESP x21) bt Tim Smyczek (USA) 6-4, 6-2, 7-6 (7/2)
Marton Fucsovics (HUN) bt Sam Querrey (USA x13) 6-4, 7-6 (8/6), 4-6, 6-2
Nicolas Kicker (ARG) bt Lukas Lacko (SVK) 6-2, 7-5, 1-6, 7-5
Dominic Thiem (AUT x5) bt Denis Kudla (USA) 6-7 (6/8), 3-6, 6-3, 6-2, 6-3
Tomas Berdych (CZE x19) bt Guillermo Garcia-Lopez (ESP) 6-3, 2-6, 6-2, 6-3
Fabio Fognini (ITA x25) bt Evgeny Donskoy (RUS) 2-6, 6-3, 6-4, 6-1
Adrian Mannarino (FRA x26) bt Jiri Vesely (CZE) 6-3, 7-6 (7/4), 5-7, 6-3
Novak Djokovic (SRB x14) bt Gael Monfils (FRA) 4-6, 6-3, 6-1, 6-3
Chung Hye-On (KOR) bt Daniil Medvedev (RUS) 7-6 (7/4), 6-1, 6-1
Julien Benneteau (FRA) bt David Goffin (BEL x7) 1-6, 7-6 (7/5), 6-1, 7-6 (7/4)
Juan Martin Del Potro (ARG x12) bt Karen Khachanov (RUS) 6-4, 7-6 (7/4), 6-7 (0/7), 6-4
Alexander Zverev (GER x4) bt Peter Gojowczyk (GER) 6-1, 6-3, 4-6, 6-3
Richard Gasquet (FRA x29) bt Lorenzo Sonego (ITA) 6-2, 6-2, 6-3
Tennys Sandgren (USA) bt Stanislas Wawrinka (SUI x9) 6-2, 6-1, 6-4
Maximilian Marterer (GER) bt Fernando Verdasco (ESP) 6-4, 4-6, 7-6 (7/5), 3-6, 6-3
Roger Federer (SUI x2) bt Jan-Lennard Struff (GER) 6-4, 6-4, 7-6 (7/4)
                  
Women's singles

2nd round

Bernarda Pera (USA) bt Johanna Konta (GBR x9) 6-4, 7-5
Barbora Zahlavova Strycova (CZE x20) bt Lara Arruabarrena (ESP) 6-3, 6-4
Maria Sharapova (RUS) bt Anastasija Sevastova (LAT x14) 6-1, 7-6 (7/4)
Agnieszka Radwanska (POL x26) bt Lesya Tsurenko (UKR) 2-6, 7-5, 6-3
Caroline Garcia (FRA x8) bt Marketa Vondrousova (CZE) 6-7 (3/7), 6-2, 8-6
Lauren Davis (USA) bt Andrea Petkovic (GER) 4-6, 6-0, 6-0
Lucie Safarova (CZE x29) bt Sorana Cirstea (ROM) 6-2, 6-4
Karolina Pliskova (CZE x6) bt Beatriz Haddad Maia (BRA) 6-1, 6-1
Hsieh Su-wei (TPE) bt Garbine Muguruza (ESP x3) 7-6 (7/1), 6-4
Aliaksandra Sasnovich (BLR) bt Mirjana Lucic-Baroni (CRO x28) 6-3, 6-1
Angelique Kerber (GER x21) bt Donna Vekic (CRO) 6-4, 6-1
Ana Bogdan (ROM) bt Yulia Putintseva (KAZ) 1-6, 6-2, 6-3
Naomi Osaka (JPN) bt Elena Vesnina (RUS x16) 7-6 (7/4), 6-2
Madison Keys (USA x17) bt Ekaterina Alexandrova (RUS) 6-0, 6-1
Ashleigh Barty (AUS x18) bt Camila Giorgi (ITA) 5-7, 6-4, 6-1
Simona Halep (ROM x1) bt Eugenie Bouchard (CAN) 6-2, 6-2