British No.1 Heather Watson survived losing to first set to defeat Romania's Alexandra Cadantu to march into the second round of the Australia Open.

The World No.50 claimed her first ever win in the opening slam of the year, 2-6 6-3 6-2, following a revival from a set and break down in the second.

But a major medical time-out for Cadantu in that second set allowed Watson time to regroup, an opportunity she took full advantage of as she broke back at 3-1 down before squaring the match.

The third set was on serve until a lengthy time-out for Watson, during which she was treated for an illness, but returned to break again; a decisive blow against her opponent ranked 91 in the world.

Heather Watson
Watson bounced into round two.

"At the beginning I definitely wasn't there," said Watson. "I wasn't playing well; I didn't have much energy today. I don't know what it was. I think I'm going to see the doctor."

"The match before was a long one and we never knew when we were going on. I was warming up for like two hours.

"When I started cramping, I had to start hitting the ball because I couldn't move. I'm kind of thankful that I did cramp today, otherwise I don't know how that would have ended up.

"I think the break did help me. It gave me time to eat, get some fuel in me and just get recharged."

In her first ever Australia Open second round match Watson will face either Mona Barthel or Ksenia Pervak.

Elsewhere in the women's draw there were wins for home favourite Samantha Stosur, Agnieszka Radwanska, Li Na and Maria Sharapova, who defeated fellow-Russian Olga Puchkova 6-0 6-0.

Andy Murray, Laura Robson and qualifier Jamie Baker all begin their campaigns on Tuesday.

Meanwhile, in the men's draw Novak Djokovic began his attempts to win a third successive crown in Melbourne by dispatching Paul-Henri Mathieu in three sets and 102 minutes on Rod Laver Court.

"It was a good performance for a first round," the world No.1 said."It's expected in the first match you're still not 100 per cent on the court.

"You're trying to, but it's going to get better with matches that I play. Hopefully I can continue on with the same rhythm."

Djokovic will face Ryan Harrison in round two after his recovery to defeat Columbian Santiago Giraldo.

There were no problems either for Tomas Berdych, who overcame Michael Russel in three sets, but No.10 seed Nicolas Almagro required five sets to fend of American Steve Johnson.

Kei Nishikori dismissed fears over a knee injury by beating Victor Hanescu in four sets after losing the first set tie-break.

"It [the knee] feels good," the No.16 seed said. "I think it's no problem. I played four sets, it's fine and it should be okay

"I had an echo (scan) a couple of days ago. I saw the picture and it showed nothing. It's good."