Complex sentence: Roger Federer won his eighteenth men's single Grand Slam title by defeating Rafael Nadal after a five-set final, which was his first major title since 2012 Wimbledon, a rematch of the 2009 Australian Open final that saw Nadal win in five sets.
Split into simpler sentences: Roger Federer won his eighteenth men's single Grand Slam title by defeating Rafael Nadal after a five-set final. It was his first major title since 2012 Wimbledon and a rematch of the 2009 Australian Open final, which Nadal had won in five sets.