DOHA (AFP) - New Australian Open champion Angelique Kerber crashed out of the Qatar Open on Tuesday, in her first singles tournament since winning in Melbourne last month.

An out-of-sorts Kerber lost her second round match - she received a first round bye - in straight sets 7-5, 6-1 to China's Zheng Saisai, who is ranked 71 places below the world number two.

In a lacklustre performance, the German lost her serve six times, hit 38 unforced errors - Saisai hit only eight - and was beaten in just one hour and eighteen minutes as her opponent dominated.

The second set took just 28 minutes as Kerber's game collapsed.

Kerber, who has not played any singles tournaments since beating Serena Williams in Melbourne on Jan 30, grew increasingly exasperated with her form on a blustery night in Doha and at one point could be heard telling her coach Torben Beltz that she was tired and had no energy.

The Poland-based German said she did not know if her poor performance was down to a lack of match fitness or not being able to respond to the new pressure of being a Grand Slam champion.

"I don't know if it was the pressure or not. I know, of course, pressures from the last years, but maybe it was both," she told reporters.

"I mean, I was feeling this morning also not good when I was practising. This is actually what I can say, I don't know how many mistakes I did today. This is not my game, to make so many mistakes.

"I was trying to go for it. I think it was more like I was not feeling my game and not finding my rhythm." A delighted Saisai plays Canada's Eugenie Bouchard in the third round.

Bouchard beat the Czech Republic's Denisa Allertova 7-6 (7-0), 7-5 as she continues her recovery from a traumatic end to 2015.

Buchard, who confirmed she is still pursuing legal action against the United States Tennis Association after she slipped and fell down in a locker room during the US Open last September, said she was just happy to be playing tennis again after several months out.

"I can't complain even if I play terrible, I'm so happy to be back on tour," she said.

"I'm really grateful. I really realised how much I missed and loved tennis when I was forced out because of my injury at the end of 2015." Earlier on Tuesday, the tournament's number three seed Agnieszka Radwanska won 6-4, 6-4 against Kateryna Bondarenko from Ukraine.

"Obviously it was hard conditions, but I won," said Radwanska afterwards.

"That's the most important thing. The first matches are always very tricky, especially the different conditions everywhere, and here in Doha as well. We used to it (being) always a bit windy and can be very tough." Also through is Petra Kvitova who won 7-6 (7-2), 6-4 against Czech compatriot Barbora Strycova.

Number two seed Simona Halep, the 2014 champion in Doha, was in action later on Tuesday against Russia's Elena Vesnina.