Stan Wawrinka of Switzerland celebrates his win against Martin Klizan of Slovakia during their men's singles first round match on day one of the Australian Open tennis tournament in Melbourne on January 16, 2017. Pic/AFP

Melbourne: Stan Wawrinka apologised for slamming a ball at Martin Klizan after he fought back from a break down in the final set to overhaul the Slovak 4-6, 6-4, 7-5, 4-6, 6-4 yesterday.