Nadal overcomes Nishikori to advance to Australian Open quarterfinals
Nadal and Victoria Azarenka roll on in style in Australian Open
The top seed won 7-6 (7-3) 7-5 7-6 (7-3) against Nishikori.
Victoria Azarenka also remained on course for a third straight Australian Open title after beating Sloane Stephens 6-3 6-2.
The Belarusian's hopes of another victory in Melbourne were boosted by third seed Maria Sharapova's surprise defeat by Dominika Cibulkova.
Jelena Jankovic, the eighth seed, is out after losing to Simona Halep, The BBC reports. (ANI)