Coco Gauff shone on her Australian Open debut on Monday as she knocked Venus Williams out of the first round in a repeat of her stunning victory over the seven-times Grand Slam champion in the Wimbledon opener last year.

The 15-year-old American sensation, 24 years Williams' junior, eased to a 7-6(5) 6-3 win in the clash of generations at Margaret Court Arena, Gauff's first main draw appearance as a direct qualifier at a Grand Slam.

After sealing the first set tiebreak when Williams struck an overhead smash into the net, Gauff broke her compatriot twice in the second before serving out the match to love.

Gauff led 5-3 and had three sets points, while a 5-2 lead in the tie-break also disappeared, but a missed backhand volley from Venus at 5-6 helped her young opponent over the line in the opener.

There were no wobbles in the second, and Gauff said: "That was really difficult, she played really well. I was really nervous for today's match. I was a bit shocked, I'm sure everybody was shocked, when they saw that draw but I'm really glad to get through it."

Gauff will face Romanian Sorana Cirstea, who earlier beat Barbora Strycova 6-2 7-6(5), for a place in the third round. 

Defending champion Naomi Osaka made a solid start to her campaign with a straight-sets victory over Marie Bouzkova.

Osaka, who beat Petra Kvitova in the final 12 months ago to win her second grand slam title, had the honour of opening the tournament on Rod Laver Arena.

There was a brief moment of alarm in the second set when she trailed 21-year-old Czech Bouzkova 4-2 but Osaka won the next four games to seal a 6-2 6-4 victory.

The third seed will next face China's Zheng Saisai, who defeated Anna Kalinskaya 6-3 6-2. 

Serena Williams eased into the second round

Serena Williams put aside her concerns about the air quality at Melbourne Park as she breezed into the second round of the to remain on course for a record-equalling 24th Grand Slam title.

Buoyed by securing her first WTA title as a mother in Auckland two weeks ago, the 38-year-old American great kept her stay out on Rod Laver Arena to a minimum with a 6-0 6-3 trouncing of Anastasia Potapova in under an hour.

The air quality was officially rated good on Monday but Williams had not forgotten the choking smoke from Australia's bushfires that greeted her when she arrived in Melbourne earlier this week.

"I definitely was concerned, and am. I think it changes every day," the eighth seed told reporters.

"It's literally every day, we are just waiting every day to see how the air quality would be ... Today, it seemed normal. Yeah, it seemed pretty good... It definitely felt like that."

Ashleigh Barty

Australia's great hope, top seed Ashleigh Barty gave her fans a scare by losing the first set to Ukraine's Lesia Tsurenko but rectified the situation quickly to win 5-7 6-1 6-1.

Barty is looking to become the first Australian woman to win the singles title since Chris O'Neil in 1978.

Petra Kvitova, who Osaka beat in a dramatic final 12 months ago, was the quickest winner of the day, taking just 50 minutes to swat aside fellow Czech Katerina Siniakova 6-1 6-0 under the roof on Margaret Court Arena.

Caroline Wozniacki began her final tournament with a 6-1 6-3 victory over American Kristie Ahn while there were also wins for 13th seed Petra Martic and 14th seed Sofia Kenin.