(Photo credit: Mike Frey-Imagn Images)

No. 2 seed and six-time Grand Slam champion Iga Swiatek didn't play her best, but it was good enough to defeat No. 31 Anna Kalinskaya 6-1, 1-6, 6-1 on Saturday to move to the fourth round of the Australian Open.

It took Swiatek, of Poland, one hour and 44 minutes to advance to the second week of the Australian Open --- the only major she has not won -- for the sixth time in eight tournaments in Melbourne.

A laser-focused Swiatek won 16 of 20 points on her service in the first set, didn't face a break point and converted two of three break chances on her Russian opponent's serve.

But after getting treatment on her back between sets, Kalinskaya found a new accuracy and Swiatek faltered in the second. Swiatek scored on just five of 18 serve attempts, made 11 unforced errors and saved only one of four breaks as Kalinskaya cruised through the set.

The third set flipped back Swiatek's way as she won 81% of points on her first serve, took a commanding 5-0 lead and saved all three break points.

'It's not surprising for me because I know that Anna can play amazing tennis,' Swiatek said. 'I didn't feel I was playing worse in the second set. I felt like she just started playing in all the balls that went out in the first.'

In the next round, Swiatek will meet Maddison Inglis, an Australian who advanced on a walkover when two-time tournament champion Naomi Osaka, the No. 16 seed, withdrew because of a left abdominal injury.

Three American women -- No. 4 Amanda Anisimova, No. 6 Jessica Pegula and No. 9 Madison Keys -- also advanced to the fourth round with straight set victories earlier Saturday.

Anisimova defeated countrywoman Peyton Stearns, 6-1, 6-4. Pegula ousted Oksana Selekhmeteva of Russia 6-3, 6-2, and Keys outslugged Czech Karolina Pliskova 6-3, 6-3.

Third-seeded Coco Gauff and No. 29 Iva Jovic advanced on the top half of the draw on Friday, giving the United States five players in the round of 16.

Keys, the defending Australian Open champion, had the toughest task, facing former world No. 1 Pliskova, who is on the comeback trail. However, Keys jumped out to an early 4-0 lead, survived one break of serve and won all four points on Pliskova's serve in the ninth game to take the first set.

The second set was more tightly contested, but Keys broke serve in the eighth game and reached the finish line in 75 minutes.

Keys has won her past 10 matches in Melbourne.

Awaiting her in a tough fourth-round match is Pegula, who advanced in 66 minutes. At 2-2, the veteran American broke her opponent's serve on a 14-point game and cruised in the first set, the finished the second set in short order.

'I felt like some things I expected to happen happened and some things I had to adjust to in the first couple games,' Pegula said. 'Her serve wasn't quite as spinny as I thought it was going to be.

'I wanted to stick to a strategy, but you know, sometimes you go out and you feel something different by the way you're hitting the ball, but luckily today, I think things worked out pretty well.'

Keys leads the series with Pegula 2-1 and has won the past two matchups. Their last meeting took place over a year ago in Adelaide, Australia, where Keys won in three sets.

'It's going to be a tough match. Jess is such a great player,' Keys said after learning of the matchup. 'She's always consistently doing so well every single week she plays. She's just so gritty.'

Anisimova has yet to play a clean match, as she served up seven double faults and made 30 unforced errors versus Stearns. Each player had eight break chances, but Stearns only capitalized on two of her opportunities.

Anisimova will play Xinyu Wang of China, who upset No. 13 Linda Noskova 7-5, 6-4.

Also heading for a fourth-round clash are No. 5 Elena Rybakina of Kazakhstan and No. 21 Elise Mertens of Belgium.

Rybakina advanced with her 6-2, 6-3 victory over Czech Tereza Valentova. Mertens ousted another Czech, Nikola Bartunkova, 6-0, 6-4.

--Field Level Media