answers: Roger Federer
context: year. Novak Djokovic won the men's singles title, defeating del Potro in the final, 6–3, 7–6, 6–3. It was his third US Open title and 14th Grand Slam, tieing Pete Sampras' record to become equal third among all-time Grand Slam champions. In women's singles, Naomi Osaka defeated Serena Williams in the final, 6–2, 6–4, becoming Japan's first ever able-bodied Grand Slam singles champion. The 2018 US Open was the 138th edition of the tournament and took place at the USTA Billie Jean King National Tennis Center in Flushing Meadows–Corona Park of Queens in New York City, New York, United States. </s> 2018 Australian Open The 2018 Australian Open was a tennis tournament played at Melbourne Park between 15–28 January 2018, and was the first Grand Slam tournament of the 2018 season. The tournament consisted of events for professional players in singles, doubles and mixed doubles play. Junior and wheelchair players compete in singles and doubles tournaments. Roger Federer was the defending champion in the men's singles event and successfully retained his title (his sixth), defeating Marin Čilić in the final, while Caroline Wozniacki won the women's title, defeating Simona Halep in the final to win her first Grand Slam. The tournament </s> 2018 Australian Open – Main Draw Wildcard Entries The 2018 Australian Open Wildcard Playoffs and Entries are a group of events and internal selections to choose the eight men and eight women singles wildcard entries for the 2018 Australian Open, as well as seven male and seven female doubles teams plus eight mixed-doubles teams. The USTA awarded a wildcard to the man and woman that earned the most ranking points across a group of three ATP/Challenger hardcourt events in the October and November 2017. For the men, the events included ATP Paris, $75K Canberra, $75K Charlottesville, $75K+H Shenzhen, €106K+H Bratislava,
question: who has won the mens single title in the australian open tennis tournament 2018