World No.1 Rafael Nadal overcame strong opposition from Japan's 16th seed Kei Nishikori to book his place in the quarter-finals.
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.