* World number one Serena upset by Spain's Muguruza
* Sister Venus falls to Slovak teenager Schmiedlova
* Djokovic eases past Frenchman Chardy in three sets
* Fourth seed Federer breezes into third round (Adds Sharapova victory)
By Robert Woodward
PARIS, May 28 It was the day when Serena and Venus Williams were supposed to re-ignite their grand slam rivalry by setting up a third round date but two young upstarts gatecrashed the family reunion at Roland Garros on Wednesday.
Instead of facing each other across the net at one of the four majors for the first time since 2009, tennis' most famous sisters were left to console each other after their French Open title aspirations lay in tatters.
Holder and world No.1 Serena Williams did not know what hit her as she was shocked 6-2 6-2 by Spain's Garbine Muguruza, that defeat coming barely an hour after her elder sister Venus fell 2-6 6-3 6-4 to Slovakian teenager Anna Schmiedlova.
On a chilly day in Paris, Serena never looked the force who has won 17 major titles. Her 20-year-old opponent broke the American's serve twice early in the first set and made the most of a series of unforced errors by a leaden-footed Williams.
The Spaniard, ranked 35 in the world, did not release the pressure and the match became a repeat of the nightmare of 2012, when Williams lost in the first round, not the glory of 2013 when she beat Maria Sharapova in the final here.
A netted return from Williams sent the Spaniard into ecstasy and even Williams's mother, Oracene, smiled as Muguruza leapt about the court. "Of course, it's amazing," Muguruza said. "I had to be really aggressive and focused.
"Today is a great day. I'm so happy," the Spaniard shouted.
Later Muguruza told a news conference: "She (Serena) said that if I continue playing like this, I can win the tournament. I said: 'I will try, I will try'.
Serena was philosophical, saying: "I don't think anything worked for me today. It was just one of those days, you can't be on (your game) every day.
"It's not the end of the world, there's always next year."
After the defeat of China's Li Na in the first round on Tuesday, it is the first time since tennis turned professional in 1968 that the top two women's seeds have failed to reach the third round at a grand slam.
It is also the third time, after 2004 and 2008, that both Williams sisters have lost on the same day at the French Open.
Seventh seed Sharapova, in Serena's quarter of the draw, also had an off day against Tsvetana Pironkova but eventually prevailed 7-5 6-2 against the Bulgarian.
Poland's Agnieszka Radwanska, at three the highest seed left in the women's draw, beat Karolina Pliskova of the Czech Republic 6-3 6-4 as the rain and night fell on Roland Garros.
The big names on the men's side of the draw suffered no problems in reaching the third round.
Novak Djokovic, the second seed, despatched Jeremy Chardy of France 6-1 6-4 6-2 while Roger Federer, seeded fourth, won 6-3 6-4 6-4 against Diego Sebastian Schwartzman of Argentina, a player he had never seen before.
Chardy, who beat Federer at the Rome Masters earlier this month, spelled out why Djokovic is fancied to end eight-times champion Rafa Nadal's reign here.
"He was simply stronger than me, bigger than me in all compartments. You're always under pressure. He knows everything. He can do everything."
Czech Tomas Berdych, the sixth seed, started slowly before beating Aleksandr Nedovyesov of Kazakhstan 6-7(4) 6-4 7-5 6-3. Eighth seed Milos Raonic got past Jiri Vesely of the Czech Republic 7-6(4) 6-4 6-1.
The Williams sisters third round showdown was knocked off the agenda when Venus was jettisoned out of the tournament.
The 29th seed, wearing long sleeves in temperatures of 14 Celsius, has never won the claycourt grand slam in 16 visits and, now 33, she may have to accept she never will.
Schmiedlova, aged 19 and ranked 56 in the world, wasted two match points on Venus's serve before the American hit wide to set up a third, and the Slovak clinched the match with a fine backhand cross court shot.
"This is the biggest win of my life," said Schmiedlova, who broke down when expressing how much Venus had meant to her when she was growing up.
Flavia Pennetta of Italy, seeded 12th, joined the Williams sisters in heading for the exit after going down 5-7 6-4 6-2 to Sweden's Johanna Larsson.
Sharapova looked frustrated with her own performance on a windy Philippe Chatrier court and she needed a heavy net cord in her favour on set point to take the first set.
Pironkova, who had a lengthy massage between the sets, stayed with the Russian until she was broken in the sixth game of the second, and Sharapova ended it in style by breaking her opponent in the final game.
Russian Mikhail Youzhny, the 15th men's seed, lost 6-0 6-3 3-6 6-4 to Czech Radek Stepanek. (Reporting by Robert Woodward, editing by Ken Ferris and Pritha Sarkar)