Angelique Kerber celebrated her 30th birthday with a straight-sets win over Donna Vekic to set up a mouthwatering Australian Open third round clash with Maria Sharapova, while Garbine Muguruza was among five seeded women to crash out.

Kerber endured a barren 2017 after claiming two grand slam titles the previous year - her first coming at Melbourne Park - but the German has made a superb start to this season and brushed Vekic aside 6-4 6-1 on a sweltering Thursday.

The crowd sang 'Happy Birthday' to the left-hander after her victory on Margaret Court Arena, but Sharapova will not come bearing gifts in a battle of two former world number ones.

Sharapova saw off 14th seed Anastasija Sevastova 6-1 7-6 (7-4) on an eventful, baking hot day which saw Muguruza become the biggest casualty in the women's draw, Hsieh Su-wei shocking the Wimbledon champion 7-6 (7-1) 6-4.

Simona Halep's ankle injury did not appear to hamper her, the world number one beating Eugenie Bouchard 6-2 6-2, but Johanna Konta, Elena Vesnina and Mirjana Lucic-Baroni were the other seeds to make early exits.

AGE JUST A NUMBER TO RESURGENT KERBER

After failing to claim a single title last year, Kerber already has a Sydney International success in the bag in 2018 and has looked ominous in the first two rounds.

Vekic was unable to spoil a landmark birthday for the left-hander, who needed only 70 minutes to stretch her winning streak to 11 matches and says she is relishing what her 30s have to hold.

The 21st seed said: "Yeah, getting older. I was waking up this morning, I said, 'Okay, the 2 is gone right now. I think I'm looking forward to the 30s. Also, I'm feeling the same as I did yesterday. I am feeling healthy. I'm still fit.

"I still enjoy my tennis. I'm not looking too much about the age, just how I'm feeling. I'm still feeling young."

MISERY FOR MUGURUZA

While Kerber has hit the ground running in 2018, the same cannot be said of Muguruza, who was stunned by the 88-ranked Hsieh.

The third seed has suffered with a thigh injury and cramps this month and took a medical timeout for blisters, but said that was not the reason for her surprise exit.

"I was wrapped and with a lot of taping, but just to try to make it better." said the Spaniard.

"I was pretty happy, because I didn't run a lot today, I didn't really feel it. It was getting to the process of really recovering. That's it."

HALEP DEFIES THE PAIN

Halep said she is still being troubled by a twisted ankle sustained in her first match against Destanee Aiava, but the top seed defied the pain to stay in the hunt for a first major title.

Bouchard racked up 26 unforced errors on Margaret Court Arena and held serve only once as Halep applied the pressure with her remarkable retrieving skills, sealing an emphatic win.

Asked about her injury, the Romanian, who will now face Lauren Davis, said: "Well, I still feel pain. Also, I couldn't practice much. But during the match, I just forgot about it. I had very tight tape [applied]. I could move.

"The most important thing is that I could play my game not thinking about the ankle. I did it great today."

SEEDS CONTINUE TO FALL

Ninth seed Konta, a 2016 semi-finalist in Melbourne, was on the end of a humbling at the hands of Bernarda Pera, the 123-ranked lucky loser winning 6-4 7-5.

Sharapova's success against 14th seed Sevastova was by no means unexpected, but Naomi Osaka's straight-sets win over 16th seed Vesnina raised eyebrows and Aliaksandra Sasnovich made light work of ousting Lucic-Baroni - seeded 28.