In a last-16 match highlighted by inconsistency on serve, second seed Williams battled to a 7-5 6-4 victory.

Holding serve was at a premium in a tight opening set but Williams finished strongly in hot conditions as she took another step towards a 23rd grand-slam title.

Despite tallying 46 unforced errors compared to just 14 from Strycova, Williams will face either Johanna Konta or Ekaterina Makarova in the quarters.

After world number one and defending champion Angelique Kerber crashed out, all eyes were on Williams at Melbourne Park.

But the six-time Australian Open champion did not convince during a bizarre first hour of tennis, with no real pattern as both players struggled to hold serve.

It was not until the fifth game that a player held serve, with Williams the first to do so and Strycova followed suit before the latter broke for a 4-3 lead, only for another break of serve to see the set levelled.

Williams earned four set points on Strycova's serve but the Czech fended off all four to hold at 5-5.

Strycova dug herself out of another hole at 0-40 in the 12th game, saving seven in total, but she could not deny Williams, who claimed the opening set at the eighth time of asking.

Williams flexed her muscles from then on, breaking serve in the fourth game after Strycova volleyed into the net as she took command of the second set.

It was relatively smooth sailing from there, despite being broken as she attempted to serve for the match, as Williams progressed to her a ninth consecutive quarter-final at a major.