World No 2 Simona Halep was dumped from the Australian Open at the first hurdle on Tuesday as China's Zhang Shuai earned her first victory in 15 Grand Slam matches.

Halep, who has been struggling with a niggling Achilles injury, had no answers to Zhang's dominant baseline game as the Chinese qualifier, ranked No 133 in the world, scored a stunning 6-4, 6-3 win in Margaret Court Arena.

The odds had been heavily stacked in Halep's favor, with Zhang having played just 14 Grand Slam matches ahead of Tuesday and losing them all - the worst record of any player in the world's top 300.

But Zhang came out firing, punishing the Romanian's scrappy service game while dominating at the net and from the baseline.

"I'm so excited that I played so well," said Zhang, who burst into tears during her courtside interview as the enormity of the upset sunk in and the crowd gave her a prolonged ovation. "I'm so happy, so excited at beating the world's No 2 player."

The 27-year-old said it was the "most memorable moment of my tennis life".

Few would given her any hope as the two walked out on court, but Halep didn't know what hit her as Zhang raced to a 4-0 lead.

The second seed finally got a break in the fifth game and looked to be clawing back into the match at 2-4, but she lost focus as Zhang pounced again to take the set.

Halep appeared to regain her composure as the second set unfolded, taking a 3-1 lead before Zhang again stepped up her game, reeling off a forehand winner.

Oldest winner

It was a huge setback for Halep, who is enjoying her highest ranking after a stellar 2015 in which she won titles at Shenzhen, Dubai and Indian Wells, raking in more than $4.5 million in prize money.

She declared before the tournament that her ultimate goal was Grand Slam glory, but that dream is now on hold.

Meanwhile, Czech qualifier Radek Stepanek became the oldest man to win a match at the Australian Open in more than 38 years.

Stepanek, 37 years and 65 days old, defeated Tatsuma Ito of Japan 6-4, 6-3, 6-7 (5), 6-2 in 3 hours, 16 minutes to advance to the second round.

He is the oldest player to have won a match at the Australian Open since Bob Carmichael (38 years and 183 days) and Ken Rosewall (44 years 62 days) in 1978.

Stepanek turned pro in 1996 and reached a career-high No 8 in 2006.

Andy Murray, a four-time finalist who is seeking his first win in Melbourne, dispatched Germany's Alexander Zverev 6-1, 6-2, 6-3 in hot conditions to move into the second round.

Afterwards the world No 2, who is awaiting the imminent birth of his first child and has pledged to race home if his wife goes into labor, immediately checked his phone for news.

"I'm hoping my phone hasn't been buzzing in my bag. My wife will message my team if anything goes on and we'll see what happens," Murray said.

Rising star Garbine Muguruza beat Estonian debutante Anett Kontaveit 6-0, 6-4 - and immediately set her sights on dethroning Serena Williams in the final.