(CNN) Serena Williams' bid for a record 24th Grand Slam title ended on Saturday when she was ousted from the French Open in the third round by US compatriot Sofia Kenin.

The 6-2, 7-5 loss came as a shock as Williams hasn't departed this early from a major tournament in five years.

"I feel like she, in that first set in particular, hit pretty much inches from the line, and I haven't played anyone like that in a long time," Williams told reporters.

Williams' exit from the Open followed another shock earlier in the day when newcomer Naomi Osaka, who surged during the last two major tournaments, lost 6-4, 6-2 to Katerina Siniakova of the Czech Republic.

Heading into the French Open, Williams and Osaka were chasing record-breaking performances, with Williams attempting to equal Margaret Court's record for the most Grand Slam singles championships and Osaka trying to become the first woman to win three consecutive major tournaments since Williams did it in 2015.

But Williams lacked matches entering the French Open, completing a mere three after her eventful Australian Open that ended with an ankle injury in a quarterfinal defeat.

Illness, but more prominently of late, a knee injury, kept her on the sidelines.

With three titles, the French Open, too, is the Grand Slam she has found most difficult to conquer.

"I'm definitely feeling short on matches, and just getting in the swing of things," Williams said, acknowledging she needed to work on her conditioning.

"I'm just pretty far away," she said. "But that's the optimistic part, is I haven't been able to be on the court as much as I would have. That's okay. At least I can start trying to put the time in now.

"It's just been a really grueling season for me."

Photos: Serena, Osaka upset Serena Williams exited the French Open on Saturday to her fellow American Sofia Kenin in the third round. Hide Caption 1 of 11 Photos: Serena, Osaka upset Williams, bidding for a 24th major, rallied in a second set but fell 6-2 7-5. A knee injury hampered the 37-year-old in the buildup. Hide Caption 2 of 11 Photos: Serena, Osaka upset Kenin, a hard-hitting baseliner, celebrated victory. The 20-year-old made the fourth round at a major for the first time. Hide Caption 3 of 11 Photos: Serena, Osaka upset It was indeed a day of shocks, as Naomi Osaka saw her 16-match grand slam winning streak come to an end. Hide Caption 4 of 11 Photos: Serena, Osaka upset The world No. 1 lost in straight sets to Katerina Siniakova, going 0-for-7 on break points and making 38 unforced errors. Hide Caption 5 of 11 Photos: Serena, Osaka upset Siniakova, 23, is a doubles world No. 1 and former junior star. She picked up her first win over a No. 1 player in singles. Hide Caption 6 of 11 Photos: Serena, Osaka upset After dropping a set in her first two matches, defending champion Simona Halep needed just an hour to breeze past Lesia Tsurenko. Hide Caption 7 of 11 Photos: Serena, Osaka upset Men's No. 1 Novak Djokovic continued to cruise. The Serb, bidding for a fourth straight major, beat Italy's Salvatore Caruso 6-3 6-3 6-2. Hide Caption 8 of 11 Photos: Serena, Osaka upset Stan Wawrinka, the 2015 champion, collected his 500th career win when he completed a 7-6 7-6 7-6 win over Grigor Dimitrov. The match had been suspended due to darkness Friday after two sets. Hide Caption 9 of 11 Photos: Serena, Osaka upset Stefanos Tsitsipas, semifinalist at the Australian Open and a winner over Rafael Nadal on clay last month, continued to progress with a four-set win over Filip Krajinovic. Hide Caption 10 of 11 Photos: Serena, Osaka upset Krajinovic, who had won his first two matches in five sets, could have played in another. He led the fourth 5-3 and held a set point in the fourth-set tiebreak. Hide Caption 11 of 11

Yet any tournament the 37-year-old plays is one she can win. She is Serena, after all.

A comeback?

And when Williams recovered from a set and break down to lead her 35th-ranked rival 5-4 in the second set, few would have bet against her.

Williams has engineered countless Grand Slam comebacks.

Her smooth, potent serve started to click and the 10th seed had the fans at Philippe-Chatrier Court behind her, especially as the feisty and fast-rising Kenin contested several line calls that appeared to rile Williams.

But her 20-year-old opponent, born in Russia, didn't buckle and broke for 6-5 in a game that began with Williams erring long on a forehand with Kenin stranded.

Williams had one more chance but sent a forehand wide on break point. Then on a second match point, her backhand sailed long.

Kenin -- who counts Maria Sharapova as her idol -- dropped her racket and during her handshake with Williams appeared to be in disbelief at what she had just accomplished.

Osaka, meanwhile, admitted the French Open was just too much to handle.

Different feeling

"Definitely I think this tournament I have had a feeling that was different to the other grand slams, or every other grand slam that I have played, because usually I find it very freeing and fun, and this time around I was kind of tense the entire time," the world No. 1 told reporters.

The fatigue Osaka said she felt playing against Siniakova might have been a result. And she suspected headaches she experienced earlier on the clay court were because of stress.

First win over a World No.1. First time into the R16 at a Slam. @K_Siniakova | #RG19 pic.twitter.com/vgAnzJ2x5e — Roland-Garros (@rolandgarros) June 1, 2019

Still, her level of disappointment at exiting the tournament so early was off the charts.

"It would go from one to 10, and I'm like at a 100 right now," said Osaka.

When Osaka remarked before the tournament that she sought a calendar year grand slam -- last achieved by Steffi Graf in 1988 -- it could have been interpreted as a tongue-in- cheek comment or at least a goal further down the road.

Osaka is only 21.

Thinking about calendar year slam

But she focused on doing it this year, which she called a mistake.

"I think I was overthinking this calendar slam," said Osaka. "For me, this is something that I have wanted to do forever. But I think I have to think about it like if it was that easy, everyone would have done it.

"I just have to keep training hard and put myself in a position again to do it hopefully."

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Osaka is adapting to the clay. But she is a quick study, evidenced by a 7-1 record on the surface this season coming into the French Open.

That combined with her performances at the US Open -- where she defeated Williams in a controversial contest -- and Australian Open suggested that another comeback would be in the cards against Siniakova.

Osaka after all rallied from set and break deficits in the first round against Anna Karolina Schmiedlova and second round against fellow grand slam champion Victoria Azarenka.

It felt like her victory over Azarenka could spark a glittering run but it wasn't to be.

The 42nd-ranked Siniakova -- No. 1 in doubles -- starred in the juniors and for her country in last year's Fed Cup final against the US.

The 23-year-old took her chances, converting three of six break points, while Osaka went 0 for 7, all in the opening set. She was also tidy from the baseline, whereas Osaka committed 38 unforced errors.

When Osaka erred on match point, Siniakova moved into the fourth round at a major for the first time like Kenin and collected a maiden victory over a No. 1.

Halep, Djokovic cruise

Siniakova downed defending French Open champion Simona Halep in China two years ago. On Saturday, Halep prevailed against Lesia Tsurenko in around an hour 6-2 and 6-1 after three-setters in her opening two outings.

Also advancing in warm and sunny conditions were men's No. 1 Novak Djokovic, three-time major winner Stan Wawrinka and fifth-seed Alexander Zverev.

Djokovic breezed past Italian qualifier Salvatore Caruso 6-3, 6-3 and 6-2 and is yet to drop a set -- or come close to it.

The Serb's own chances of completing a calendar year grand slam are still on and if he wins the title, Djokovic would hold all four majors for the second time in his career.

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The man he lost to in the 2015 final, Wawrinka, collected his 500th career victory by completing a win over Grigor Dimitrov 7-6 (5), 7-6 (4) and 7-6 (8). They were forced off due to darkness following two sets Friday on the soon to be replaced Court 1.

Wawrinka -- who trailed 6-2 in the final tiebreak -- also accomplished a career grand slam of victories over Dimitrov.

The Swiss meets Greek sixth-seed Stefanos Tsitsipas in an eagerly anticipated battle of one-handed backhands Sunday.

Five-set battles are no surprise for Zverev at Roland Garros. He improved to 5-0 by defeating Monte Carlo finalist Dusan Lajovic 6-4, 6-2, 4-6, 1-6 and 6-2 a year after they went the distance in Paris.

Zverev's fellow German, Jan-Lennard Struff, won the longest match of the day in four hours, 22 minutes, upsetting 13th-seed Borna Coric 4-6, 6-1, 4-6, 7-6 (1) and 11-9.

Coric went a mere 4-20 on break points. When he did break at 6-6 in the fifth, he was immediately broken back.