Tsvetana Pironkova

Williams, who turned 39 on Saturday, took her time to warm up on a cool Monday in Paris, Kristie Ahn making life particularly difficult for the sixth seed in a well-contested opening set.

The American duo had also met in the opening round of the US Open and - as was the case in New York - the favourite eventually prevailed in straight sets,meaning a clash with another familiar foe next.

Pironkova threatened to cause an upset when they did battle in the quarter-finals at Flushing Meadows earlier this month, though faded down the stretch to lose in three.

Still, Williams - chasing a 24th slam to move level with Margaret Court's record - expects another tough test from the Bulgarian, who defeated Andrea Petkovic 6-3 6-3.

"She's playing well, but I am too. I'm ready to play her. She'll be ready to play me," the three-time French Open champion said in her post-match press conference. 

"It will be a long match, she will get a lot of balls back, but so am I. I'll be ready."

Williams revealed she was a little flat against Ahn in a first set that went to a tie break, before a more positive approach allowed her to breeze through the second without dropping a game.

"The biggest difference was just confidence. I just need to play with more confidence, like I'm Serena," she said. "So that was it. I just started playing like that. And I love the clay and I started playing like it, opening the court and moving and sliding."

SUCCESS FOR SEEDS ON DAY TWO

Three other top-10 seeds at the tournament avoided early exits. Elina Svitolina, Kiki Bertens and Petra Kvitova prevailing, though none of the trio had it all their own way.

Bertens was in danger of going home early when the fifth seed fell a set behind but rallied impressively to see off Katarina Zavatska 2-6 6-2 6-0.

Seventh seed Kvitova overcame Oceane Dodin 6-3 7-5, though admitted afterwards her opponent had made her work for the win.

"You know, she didn't make that many mistakes and it was really a tough one," Kvitova - a semi-finalist at Roland Garros in 2012 - told the media. "I just really tried to stay there mentally strong and wait for the chance to break her and serve well."

Meanwhile, Svitolina, the third seed, triumphed 7-6 (7-2) 6-4 against Russian Varvara Gracheva.

KEYS LOST IN FRENCH CAPITAL, KERBER CRASHES OUT

Madison Keys, the 12th seed, was on the wrong end of an upset, the American beaten in straight sets by Zhang Shuai.

Prior to that match on the same court, 15th seed Marketa Vondrousova was crushed by Iga Swiatek of Poland, winning just three games in a surprisingly lopsided contest that spanned just 63 minutes.

Angelique Kerber also suffered a shock exit, the three-time major winner going down 6-3 6-3 to world number 102 Kaja Juvan.

Karolina Muchova was also dumped out, going down to Christina McHale, but 2016 champion Garbine Muguruza avoided a similar fate against Tamara Zidansek, overcoming a one-set deficit to eventually prevail 5-7 6-4 8-6.

Williams and Halep played in an exhibition event with a crowd of 4,000 watching on in Adelaide last Friday and they were back in competitive action three days later.

Legendary American Williams beat Daria Gavrilova 6-1 6-4 to move into the third round of the Yarra Valley Classic.

The fifth seed struck 27 winners to 15 unforced errors on Margaret Court Arena as she set up a meeting with Tsvetana Pironkova, who ousted Donna Vekic 1-6 6-4 6-2.

Williams said: "It was a good match for me. It wasn't easy at all. It was lots of rallies and lots of movement, and she's from here, so she obviously always plays hard. So it was really good and it felt good to clinch that in the end."

Third seed Karolina Pliskova, Petra Martic, Danielle Collins and Marketa Vondrousova also advanced to the last 16 on Monday.

Elsewhere, top seed Halep is through to the third round of the Gippsland Trophy following a 6-4 6-4 win over Anastasia Potapova.

Halep hit 23 winners and broke twice in each set in what was her first official match since October.

Elina Svitolina, the third seed, beat Andrea Petkovic 6-1 6-4, while Coco Gauff, Ekaterina Alexandrova and Jelena Ostapenko were among the other winners seven days prior to the start of the first grand slam of 2021.

Azarenka was pushed before the two-time Australian Open winner booked her spot in the last eight at Flushing Meadows.

Williams was also challenged before reaching the quarter-finals and her bid for a record-equalling 24th grand slam singles title remains on track.

But there was no such luck for this year's Australian Open champion as Kenin bowed out.

AZARENKA BATTLES THROUGH AS KENIN FALLS

Azarenka reached the US Open quarter-finals for the first time since 2015 after overcoming Czech 20th seed Karolina Muchova 5-7 6-1 6-4.

Muchova was on top early before Azarenka steadied to advance in two and a half hours.

The Belarusian, twice a US Open runner-up, was eventually too good for Muchova, who battled a leg injury late in the last-16 clash.

Azarenka won the Western & Southern Open ahead of the US Open, showing some good form since the WTA Tour season restarted amid the coronavirus pandemic.

She will next face Elise Mertens after the Belgian 16th seed proved far too good for Kenin – the second seed – 6-3 6-3 in just 75 minutes.

Mertens hit 19 winners and just seven unforced errors against Kenin, whose best run at her home slam came to an end.

The win saw Mertens reach the quarters for the second straight year.

SERENA SURVIVES SCARE

Williams came through a tough battle with Maria Sakkari, winning 6-3 6-7 (6-8) 6-3 after two hours, 28 minutes.

The American star looked set to endure more frustration in her quest to level Margaret Court's record when she trailed Sakkari by a break in the third set.

Sakkari came from a set down to defeat Williams at the Western & Southern Open.

However, she could not hold on to her advantage in the decisive set as Williams produced a response befitting her status as a 23-time major champion.

"Just felt like I was able to compete longer. I was a little fatigued last time and had some cramps, but I felt like Maria played a completely, I felt like she almost played better today. She's such a good competitor," Williams said.

"It was a really intense match."

PIRONKOVA'S FAIRYTALE RUN CONTINUES

Awaiting Williams in the quarter-finals is Tsvetana Pironkova, whose run continued with a 6-4 6-7 (5-7) 6-3 victory over Alize Cornet.

A former Wimbledon semi-finalist, Pironkova is back playing for the first time since 2017.

The Bulgarian has put together an impressive run in New York, where she had only reached the fourth round once previously – in 2012.

Williams' pursuit of a long-awaited record-equalling 24th major title appeared in serious trouble as she struggled to effectively combat the resurgent Pironkova's combination of forehand slice and backhand power.

The Bulgarian - a 2010 Wimbledon semi-finalist - had not appeared on the WTA Tour since playing the All England Club three years ago but dumped out two seeds en route to this stage.

As the finish line quickly moved into sight on Arthur Ashe, though, the great Williams proved a step too far for Pironkova.

The 38-year-old, beaten in the previous two Flushing Meadows finals, dug in for an exhausting 4-6 6-3 6-2 success and set up her latest semi against either Elise Mertens or Victoria Azarenka.

Williams is aiming to win a grand slam for the first time since giving birth to her daughter in 2017, having lost four major finals in the intervening period as she remains one championship shy of Margaret Court's record 24.

Yet Pironkova's story heading into their last-eight meeting was perhaps even more remarkable still.

The Bulgarian, who had a son in 2018, was playing for the first time since Wimbledon three years ago and incredibly defeated two seeds en route to meeting Williams.

She had control of this latest clash for long periods, too, leading by a set and a break at one stage, but Williams rallied to triumph 4-6 6-3 6-2.

The 38-year-old gushed in her praise of Pironkova afterwards, however, saying in her on-court interview: "It just shows me how tough moms are.

"Whenever you can birth a baby, then honestly you can do anything. I think we saw that with Tsvetana today. She played unbelievable.

"[Playing for the first time since 2017] is unbelievable. Wow. I couldn't even do that. I could barely win a match when I came back. She's incredible.

"That's why I say I'm most influenced by moms. Like how do you do it?

"You play a match, you go home and you're still changing diapers. It's like a double life. It's really surreal."

Williams will now take on Elise Mertens or Victoria Azarenka in the semi-finals on Thursday and is targeting a faster start.

She said: "I play again tomorrow. The good news is I'm used to playing back to back to back to back to back, so in a way I'd kind of be used to it.

"But at the same time, I need to work out how to start a little bit faster."