Every defeat, even to the world number 1, is a bitter disappointment for Shahar Pe’er.The 23-year-old Israeli was thrashed 6-2, 6-2 by Serena Williams in the fourth round at Roland Garros on Monday, ending her superb run in Paris.Pe’er was playing in the last 16 of a Grand Slam tournament for the first time since Wimbledon in 2008 and despite the defeat is guaranteed of at least equaling her career-best ranking of number 15.However, Pe’er had hoped for a better showing in her first ever appearance on Court Philippe Chatrier and told The Jerusalem Post of her frustration at falling to 0-5 in her career against Williams.“These are matches you want to win regardless of the opponent,” Pe’er said. “It’s disappointing, but this is part of the life of a tennis player.”The Israeli believes she knows exactly what is missing from her game so that she will give the likes of Serena a fight next time they meet.“I need to learn to be more aggressive and make the most of my chances,” said Pe’er, who made 21 unforced errors and was broken nine times in the brief 67-minute-long match. “I must be able to take the initiative in the points.” Pe’er got the match off to a dream start, breaking Williams to love. The top seed was spraying her shots all over the place at the start of the encounter and Pe’er won the first seven points.However, from a 0-40 deficit in the second game, Williams reeled off the next nine points, holding to love with a backhand winner to take a 2-1 lead.Pe’er quickly tied the score, but in the fifth game she once more failed to take a point on Serena’s serve and the Israeli would not take another game in the first set.Williams broke Pe’er at will, and after 28 minutes Shahar sent a backhand slice into the net and the American wrapped up the first set.Pe’er had to dig deep to hold her first game of the second set and tie the score at 1-1, but she then squandered two break points in the third game before dropping her serve yet again.The Israeli put up a brave fight to break back with a backhand winner down the line in the subsequent game, but it would be her last hurrah. Williams took the next three games and clinched victory with a love service game after Pe’er buried another forehand in the net.Williams was very pleased with the way she played.“I seem to always be able to turn it up during this particular stage of the tournament,” she said. “I felt really powerful today and strong and able to dictate.” Despite the defeat, Pe’er, who has now lost all 10 of her meetings against the Williams sisters, was pleased with her overall performance in Paris.“I had an excellent clay court season and I’m hoping to continue this momentum during the rest of the year,” said Pe’er, who will play in Eastbourne in a couple of weeks before taking part in Wimbledon.But before she turns her attention to the grass, Pe’er has still got some unfinished business in the doubles tournament at Roland Garros.Pe’er and Monica Niculescu beat No. 10 seeds Yung-Jan Chan and Jie Zheng 6-2, 6-1 to advance to the quarterfinals on Monday where they will face No. 2 seeds Nuria Llagostera Vives and Maria Jose Martinez Sanchez on Tuesday.“We enjoy ourselves on court and we get along really well,” Pe’er said of her new doubles partner. “We are facing a tough match, but anything is possible. We are playing well and have already beaten two seeds so you can’t tell what might happen.”Also Tuesday, Andy Ram and Julian Knowle, seeded No. 10 in the men’s doubles event, play Brazilians Marcelo Melo and Bruno Soares in the last eight.In other fourth round action, Sam Stosur ended Justine Henin’s hopes of a comeback victory by converting a second match point on Monday for a 2-6, 6-1, 6-4 victory, while Rafael Nadal and Novak Djokovic were winners on the men’s side.Stosur will play Williams in the quarterfinals.“Obviously beating Justine is going to give me lot and lots ofconfidence,” said Stosur, seeded No. 7. “It’s a great achievement forme, but it’s not over yet. I’m just in the quarters and going to playthe No. 1 player in the world next.”Nadal, another four-timechampion, advanced by beating No. 24-seeded Thomaz Bellucci 6-2, 7-5,6-4. The Spanish player, who lost in the fourth round in 2009, has yetto drop a set in this year’s tournament and will next play compatriotNicolas Almagro, seeded 19th.Third-seeded Djokovic eliminated the last American in the men’s draw, Robby Ginepri, 6-4, 2-6, 6-1, 6-2.Elsewhere,No. 4 Jelena Jankovic committed only 11 unforced errors in her 6-4, 6-2defeat of No. 23 Daniela Hantuchova, and will meet unseeded YaroslavaShvedova in the quarterfinals.Djokovic’s next opponent will be No. 22 Jurgen Melzer, a first-time Grand Slam quarterfinalist playing in his 32nd major event.Shvedova became a Grand Slam quarterfinalist for the first time by beating wild card Jarmila Groth 6-4, 6-3.