answers: Roger Federer
context: 2018 Australian Open – Men's Singles Roger Federer was the defending champion and successfully defended his title, defeating Marin Čilić in the final, 6–2, 6–7, 6–3, 3–6, 6–1. It was Federer's 20th Grand Slam singles title and record-equalling sixth Australian Open men's singles title (tied with Roy Emerson and Novak Djokovic). With the win, Federer became the first male player to win at least six titles at two Grand Slam tournaments (six at the Australian Open and eight at Wimbledon). Federer became the oldest man to win a Grand Slam singles title in the Open era since Ken Rosewall in </s> his years-long quest since his 2012 Wimbledon title win for his 18th Grand Slam singles title, which previously saw three finals appearances and losses all to then-reigning No. 1 Novak Djokovic at the 2014 Wimbledon, 2015 Wimbledon and the 2015 US Open. At 35 years and 174 days of age, Federer became the second-oldest winner of a Grand Slam after Ken Rosewall since 1972. Considered altogether along with his return from his six-month injury layoff, his 2017 Australian Open run seeing three 5-set match wins over top 10 players, and his Grand Slam match history of losses against Nadal, Federer's </s> It was the first time since the 2011 Australian Open that Federer and Nadal were the top 2 seeds at a grand slam. This was the first time since the 2008 Wimbledon Championships that two unseeded players (Chung Hyeon and Kyle Edmund) reached the semifinals of the men's singles event at a Grand Slam tournament, and the first time at the Australian Open since 1999. Chung became the first South Korean player to reach the quarterfinals and semifinals of a Grand Slam event. Djokovic's fourth-round loss to Chung was his first straight-sets loss at the Australian Open since 2007. 2018
question: who won the australian men 's open final