Wawrinka continued his dominant Grand Slam form at the US Open, with wins over Albert Ramos, Chung Hyeon, Ruben Bemelmans, Donald Young. He then beat South African Kevin Anderson in straight sets in the quarterfinals to advance to the semifinals, where he was dispatched in straight sets by Roger Federer. Wawrinka then helped Switzerland advance to the Davis Cup World Group with a five-set win over Dutchman Thiemo de Bakker in Geneva. He then competed in the Rakuten Japan Open Tennis Championships, entering as the first seed. Wawrinka avenged his loss to Tatsuma Ito at the same tournament the previous year by defeating him in the second round. He eventually advanced to the finals, where he beat Benoît Paire in straight sets and won his fourth title of the season. Wawrinka then entered the Shanghai Rolex Masters, where he defeated former US Open champion Marin Čilić in a three-set battle before losing in straight sets to Rafael Nadal in the quarterfinals. Playing in the Paris Masters, Wawrinka avenged his previous loss to Rafael Nadal in Shanghai with a two set victory. In the semifinals, Wawrinka lost to Novak Djokovic in a three set match. He then matched his performance at the ATP World Tour Finals the previous year by reaching the semifinals in London with round-robin wins over Andy Murray and David Ferrer. In the semifinals, Wawrinka played Roger Federer for the fifth time in the 2015 season, losing in straight sets.