Serena Williams said Wednesday she was feeling relaxed and striving to find the right balance to avoid dips in concentration as the 23-time Grand Slam champion continued her ominous form at the Australian Open.

The 39-year-old maintained her unbeaten run since emerging from 14-day quarantine with a 6-3, 6-0 second-round drubbing of Nina Stojanovic in 69 minutes.

She said her near-flawless second set was fuelled by a carefree approach. 

"I wasn't thinking as much in the second, as I was in the first," said the American, who hit 27 winners. 

"I just think when I'm not thinking it's more or less like I'm just totally relaxed. 

"Even with my serve, I overthink it. But when I don't think about it... it goes in."  

Williams, however, was conscious about not letting her focus wander.  

"It's a balance because sometimes that's a... time to slack off and to lose focus," she said.  

"So, it's really about finding that key balance there for me." 

The 10th seed has appeared sharp and in strong form so far as she chases Margaret Court's record Grand Slam tally of 24. 

Williams started with a sizzling backhand winner and maintained a vice-like grip over the Serb, breaking in the opening game of the second set and sealing victory with her sixth ace.

The seven-time Australian Open champion has been battling shoulder and Achilles niggles but shown no ill-effects on court and appeared at ease amid the hot conditions on Rod Laver Arena, with temperatures reaching 31 Celsius (87.8 Fahrenheit).  

"The conditions were fine...I live in Florida," she said. "It was bright for me more than hot.  

"But I know it can get really hot here. I thought it was good conditions for me." 

Williams reprised her multi-coloured, one-legged catsuit -- a flamboyant outfit inspired by late sprint queen Florence Griffith Joyner, popularly known as 'Flo-Jo'.  

"This is one of my favourites, definitely top three for me," she said. "I just kept pushing the design team at Nike and then they pushed themselves and they came up with something really fabulous."

Playing her unparallelled 100th Australian Open match, she had thrashed Laura Siegemund 6-1, 6-1 in the first round and faces Anastasia Potapova of Russia next.