Angelique Kerber believes she is reaping the rewards for fighting hard to forget a miserable 2017 after battering Maria Sharapova to reach round four of the Australian Open.

The German rose to world number one during a 2016 that yielded success in Melbourne and at the US Open, but she plummeted down the rankings after failing to match those standards last season.

Kerber has started this year well, though, and was in imperious form to defeat Sharapova 6-1 6-3 on Rod Laver Arena.

And the 30-year-old says she has been putting in the hours in training to rediscover her best form.

"I just knew before the match it would be a tough one, Maria is a champion and played really good the last few weeks," she said on court.

"I'm so happy we have 2018 and not 2017 anymore, I'm so happy right now. I learnt a lot from the last 24 months, I had a great 2016, last year was a little tougher.

"Everyone who knows me knows I never gave up. I had a really tough off-season, really happy to be here playing against the best players."