The 2015 US Open was a tennis tournament played on outdoor hard courts. It was the 135th edition of the US Open, the fourth and final Grand Slam event of the year. It took place at the USTA Billie Jean King National Tennis Center.

Marin Čilić is a Croatian professional tennis player. Čilić has won 20 ATP Tour singles titles, including a major at the 2014 US Open. He was also runner-up at the 2017 Wimbledon Championships and the 2018 Australian Open, and won a silver medal at the 2020 Tokyo Olympics in the men's doubles tournament partnering Ivan Dodig. His career-high singles ranking is world No. 3, achieved on 28 January 2018. Čilić has reached the semifinal stage or better at all four majors, and the quarterfinal stage or better at all nine ATP Masters 1000 tournaments. He is one of six active players with at least 20 ATP Tour titles and one of the five active players to reach at least the semifinal stage at all four majors. Alongside compatriot Goran Ivanišević, Čilić is widely considered to be one of the greatest Croatian tennis players in history.