She progressed alongside fellow American Coco Gauff, who bounced back from a set down to defeat Sorana Cirstea 4-6, 6-3, 7-5 and extend her maiden appearance at the Melbourne major. Gauff will face defending champion Naomi Osaka in the next round after she beat Zheng Saisai 6-2, 6-4.
Top seed Ashleigh Barty beat Polona Hercog 6-1, 6-4 to clinch her place in the third round, while Aryna Sabalenka and Petra Martic—seeded 11th and 13th, respectively—were knocked out of the running.
Men's second seed Novak Djokovic breezed past Tatsuma Ito 6-1, 6-4, 6-2, while No. 6 Stefanos Tsitsipas qualified with a walkover past Philipp Kohlschreiber, whose tournament was ended by a thigh injury.
Tsitsipas remains on course to meet Djokovic in the quarter-finals but must first get the better of Milos Raonic, who beat Cristian Garin 6-3, 6-4, 6-2 to set up a clash with the Greek star.
Elsewhere, Roger Federer sauntered to a 6-1, 6-4, 6-1 win against Filip Krajinovic and will face Australian John Millman in the next round.
Wednesday's Key Results
(2) Novak Djokovic bt. Tatsuma Ito: 6-1, 6-4, 6-2
(3) Roger Federer bt. Filip Krajinovic: 6-1, 6-4, 6-1
(6) Stefanos Tsitsipas bt. Philipp Kohlschreiber (walkover)
(14) Diego Schwartzman bt. Alejandro Davidovich Fokina: 6-1, 6-4, 6-2
(24) Dusan Lajovic bt. Marc David Polmans: 6-2, 6-4, 6-3
(32) Milos Raonic bt. Cristian Garin: 6-3, 6-4, 6-2
Tennys Sandgren bt. (8) Matteo Berrettini: 7-6 (7), 6-4, 4-6, 2-6, 7-5
Tommy Paul bt. (18) Grigor Dimitrov: 6-4, 7-6 (6), 3-6, 6-7 (3), 7-6 (3)
Marin Cilic bt. (21) Benoit Paire: 6-2, 6-7 (6), 3-6, 6-1, 7-6 (3)
Yoshihito Nishioka bt. (30) Dan Evans: 6-4, 6-3, 6-4
(1) Ashleigh Barty bt. Polona Hercog: 6-1, 6-4
(3) Naomi Osaka bt. Zheng Saisai: 6-2, 6-4
(7) Petra Kvitova bt. Paula Badosa: 7-5, 7-5
(8) Serena Williama bt. Tamara Zidansek: 6-2, 6-3
(14) Sofia Kenin bt. Ann Li: 6-1, 6-3
(27) Wang Qiang bt. Fiona Ferro: 6-1, 6-2
Coco Gauff bt. Sorana Cirstea: 4-6, 6-3, 7-5
Carla Suarez Navarro bt. (11) Aryna Sabalenka: 7-6 (6), 7-6 (6)
Julia Gorges bt. (13) Petra Martic: 4-6, 6-3, 7-5
Caroline Wozniacki bt. (23) Dayana Yastremska: 7-5, 7-5
Heather Watson bt. Kristyna Pliskova: 4-6, 6-3, 6-1
Visit the Australian Open website to see the full results.
Williams survived a wobble in the second set of Wednesday's matchup to continue her march towards a possible 24th Grand Slam, despite Zidansek's best efforts to cause an upset.
The Slovenian hopeful was blown away in a one-sided first set but made things more competitive in the second. Any hope of a comeback seemed to drain away at 3-3 in the latter, however, when Zidansek failed to convert three break points before losing the final four games of the match.
Williams, 38, was knocked out by Karolina Pliskova in the quarter-finals of this competition 12 months ago, but her form in Melbourne thus far could lay the foundations of another title run:
Her latest victory denied Zidansek her maiden appearance in the third round of a major, while Williams will feature in the third stage of the Australian Open for the 18th time in her career.
But to claim victory, Williams will have to cut out the mistakes, as she acknowledged in her post-match interview (h/t Agence France-Presse): "I made so many errors in a row and had to battle through my own internal problems. I knew I had to play better and couldn't keep making unforced errors like that, otherwise it was going to be a long evening for me."
At the other end of the age spectrum, 15-year-old Gauff showed remarkable fortitude to surge back and beat Cirstea to a third-round berth:
Gauff's first appearance in this tournament has seen her already move within one step of matching her best finish at a major thus far (fourth round of Wimbledon 2019), though Osaka stands in the way of that feat.
Zheng suffered three breaks in each of their two sets played, while 22-year-old Osaka was far from her best.
However, tennis writer Jose Morgado highlighted the conditions played a part in disrupting her usual rhythm:
Barty came through her clash against Hercog with flying colours, though it helped that her Slovenian foe contributed 30 unforced errors across the two sets.
Djokovic also made his way into the next stage of the tournament with a straight-sets victory, beating Ito in a little more than 90 minutes:
He'll face another Japanese star, Yoshihito Nishioka, in the third round and looks to be worthy of a title defence based on the form he's displaying, per sportswriter Sacha Pisani:
Federer looked far from 38 years of age when he swept Krajinovic at Rod Laver Arena, where the former was every bit the superior and qualified for the Australian Open third round for the 21st year in a row.
Unseeded John Millman topped No. 30 Hubert Hurkacz 6-4, 7-5, 6-3 to set up a meeting with the Swiss, who suggested his next opponent may even have the edge in this heat, per The New York Times' Christopher Clarey:
Millman has defeated Federer once in their three career meetings overall, though he and Federer share a split record of one win apiece on hard courts.
Tsitsipas and Raonic will face each other next, and the former will hope his walkover result against Kohlschreiber leaves him well-rested for what promises to be a tough test against the Canadian.
Raonic recorded 19 aces in his straight-sets win over Garin and won 92 percent of his first-service points, indicating the final men's seed could be a dark horse threat.