Angelique Kerber lamented her defensive approach during Wednesday's second-round win at the Australian Open as the defending champion and world number one sought improvement.

In an all-German affair on Rod Laver Arena, Kerber celebrated her 29th birthday by beating Carina Witthoeft 6-2 6-7 (3-7) 6-2 to progress to the third round.

Kerber was not at her best but used her strong defensive game and benefited from Witthoeft's 69 unforced errors to stay on track for consecutive titles at Melbourne Park.

Speaking afterwards, Kerber bemoaned her 34 unforced errors as she blamed the performance on being too defensive.

"I was making a lot of mistakes, like in the important moments. But at the end, I'm happy that I won the match," the two-time grand-slam champion told reporters.

"It was not so easy. The conditions were also a little bit difficult.

"At the end, I won, and this is all that counts for me."

"Of course it was not so easy, especially also with the sun from the one side. But at the end, I was trying my best," she added.

"I'm through to the next round. I'm looking forward to being now in the third round."

Kerber continued: "I was a little bit too defensive, so I think that was the problem. When I was trying, I did few more mistakes.

"I will try for the next round to really focus on playing consistent from the first until the last point and not having too much up and downs during the match."