Day Four of the US Open came with a considerable number of upsets as more big names were in action at the Flushing Meadows.

Here's a recap of the highlights of the day:

Andy Murray’s comeback from hip surgery came to an end in the second round after a 6-2 6-3 6-4 defeat to Canadian Felix Auger-Aliassime.

Birthday Dominic Thiem served up a masterclass of ball striking and placement as he defeated Indian Sumit Nagal 6-3 6-3 6-2. The Austrian will next face 2014 champion Marin Cilic, who overcame Slovakia’s Norbert Gombos 6-3 1-6 7-6(2) 7-5.

Hungarian Marton Fucsovics claimed nine of the last 10 games to beat Bulgaria’s 14th seeded Grigor Dimitrov 6-7 7-6 3-6 6-4 6-1 in a match that lasted four hours and 50 minutes on Court 12.

Russian Daniil Medvedev, who finished runner-up to Rafa Nadal last year, cruised into the third round with a 6-3 6-2 6-4 victory over Australia’s Christopher O’Connell in a match that was played under the roof at Louis Armstrong Stadium.

Elsewhere, reigning Australian Open champion Sofia Kenin won her second-round match at the U.S. Open against unseeded Leylah Fernandez 6-4, 6-3.

Seeded No. 2, Kenin had more winners than unforced errors and never faced a break point. The American has lost in the third round at the Open each of the past three years, and will try to snap that streak Saturday.

The player she beat in the final in Melbourne earlier this year, Garbine Muguruza, was a shock second round loser, going down 7-5, 6-3 to Bulgaria's Tsvetana Pironkova, who is playing her first tournament in more than three years after taking time out to have her first child.

British number 1, Johanna Konta was also a casualty, losing 2-6 7-6 6-4 to world number 77 Sorana Cirstea.

Meanwhile, Serena Williams moved a step closer to a record-equalling 24th grand slam title with a straight-sets win over Russian Margarita Gasparyan.