Defending champion Angelique Kerber has overcome a mid-match meltdown on her 29th birthday against fellow German Carina Witthoeft before advancing to the third round of the Australian Open.

Kerber needed two hours and eight minutes to see off the staunch challenge from Witthoeft and win 6-2 6-7 (3-7) 6-2.

The world No.1 conceded the last six points of the tiebreak and the first five points of the third set before regrouping.

It was the 10th successive occasion Kerber had beaten a German opponent, but this time she did it the hard way.

“I’m 29 and getting older but I think I will have a great day,” said Kerber, who was serenaded with a rousing chorus of Happy Birthday by the crowd at Rod Laver Arena.

Witthoeft made a dreadful start to the match, double-faulting six times in her opening two service games.

But after scorching through the second-set tiebreak and going on a run of 11 straight points the free-swinging 21-year-old threatened to cause a huge boilover, only for Kerber to regroup in the nick of time.

“It’s a completely new situation for me (being the defending champion) but I think that I’m dealing with it very well and enjoying it,” said Kerber, who will play either No.27 seed Irina-Camelia Begu from Romania or Czech Kristyna Pliskova in the round of 32.