Britain's dreams of Wimbledon glory came to an end on just the fourth day of the tournament as Tim Henman and Katie O'Brien lost their second-round matches.

The pair were the only British players to reach the second round, but they were beaten by Feliciano Lopez and Michaella Krajicek respectively.

O'Brien, who was on court at 11am, was the first to fall, picking up just one game as she was beaten 6-0 6-1 by the 31st seed.

Henman at least thrilled Centre Court for a while with a fightback to force Lopez into a fifth set after the Spaniard had won the first two on tie-breaks.

Lopez faded as Henman won the third and fourth sets at a canter, but two breaks of serve in the fifth set saw the man from Madrid turn the match on its head once more and he came through 7-6 7-6 3-6 2-6 6-1.

Despite his defeat, Henman vowed to return to SW19 next year.

"Absolutely," said Henman, when asked if he planned to return for another series of nail-biters next year.

"I will reflect on the two matches I've played (at Wimbledon). That is the tennis I want to play more regularly.

"There's no reason why I can't do that. I'm not going to play forever, but I'm passionate about what I do. I love what I do. I want to make the most of it."

Elsewhere Roger Federer took just 11 minutes to complete his 50th straight victory on grass.

Leading Argentinian teenager Juan Martin Del Potro by two sets to love and 2-0 in the third overnight, the defending champion quickly wrapped up a 6-2 7-5 6-1 win to seal his place in the third round.

Next up for Federer will be a showdown with talented Russian Marat Safin, the man who beat the Swiss in the 2005 Australian Open semi-finals. Safin beat Aisam-ul-Haq Qureshi in straight sets.

Rafael Nadal will meet Robin Soderling in the third round after a routine success against Werner Eschauer.

Despite not being at his best, the second seed dropped only seven games, winning six in succession to win both the first and third sets. Soderling earlier beat Sebastien Grosjean in four sets.

The last man to win Wimbledon prior to Federer's four-year reign, Lleyton Hewitt, booked his place in the third round with a comprehensive defeat of Simone Bolelli.

With his forehand in particularly fine form, Hewitt broke his opponent seven times while Bolelli failed to convert any of his four break-point opportunities as the Australian romped to a 6-2 6-2 6-1 victory.

Last year's semi-finalist Marcos Baghdatis and recent Halle winner Tomas Berdych both won in four sets, while fellow seeds James Blake, Tommy Haas and Ivan Ljubicic all cruised into the last 32 with straight-sets wins.

But it was not all plain sailing for the seeds.

Both sixth seed Nikolay Davydenko and Mikhail Youzhny (14) were taken the distance, the former coming back from two sets down to scrape past the big-serving Australian Chris Guccione.

Guccione's compatriot Wayne Arthurs' career will continue for one more match at least after he took out 11th seed Tommy Robredo.

The 36-year-old will retire after Wimbledon but he was in no mood to finish up on Thursday.

Robredo had no answers to Arthurs' big-serving game and was unable to break in the match as he slumped to a 6-3 7-6 (7/5) 6-3 defeat.

Arthurs will now face fellow veteran Jonas Bjorkman for a place in the last 32.

Joining Robredo through the exit door on Thursday were three other seeds who prefer the slower claycourts.

Robredo's fellow Spaniard David Ferrer, the 17th seed, was beaten 6-3 6-4 6-3 by in-form Frenchman Paul-Henri Mathieu; 24th seed Juan Ignacio Chela was also a straight-sets loser, going down 7-6 (7/3) 6-4 7-5 to France's Edouard Roger-Vasselin; and Agustin Calleri (29) bowed out to Hyung-Taik Lee, the Korean emerging from Court 10 as a 7-6 (8/6) 6-4 6-7 (3/7) 6-3 winner.

In the ladies' singles, Maria Sharapova led the way on another good day for the seeds.

Aside from a 17-minute opening game of the second set, Severine Bremond offered little resistance, going down 6-0 6-3.

Defending champion Amelie Mauresmo also lost just three games as she swept past Yvonne Meusburger in impressive fashion.

The fourth seed strolled to a 6-1 6-2 victory on Court Two, an arena which has earned the nickname of the Champions' Graveyard over the years, but there was little chance of an upset in this match.

Three-time former champion Venus Williams breezed past Hana Sromova as she improved on her sluggish first-round performance.

The 2000, 2001 and 2005 winner was on the brink of defeat against unknown Russian Alla Kudryavtseva, but looked much more focused this time.

In the end the American, seeded 23 this year, took just 51 minutes to wrap up a 6-2 6-2 win.

Sixth seed Ana Ivanovic continues to make steady progress at the All England Club as she swept aside Meilen Tu.

Play started at 1100 BST to try and make up for Wednesday's rain delays and the French Open runner-up wasted no time in booking her third-round spot with a comfortable 6-4 6-3 victory over Tu in the morning.

Ivanovic's best results in the past have come on clay but she believes she is getting to grips with the grass.

She said: "It's a different game, a different kind of movement. It takes some time to adjust to it but now I'm starting to feel better on the court. I feel I'm moving well.

"I just want to play my game, try to be more aggressive, which I think can be very useful on the grass."

But she does not feel she should be mentioned among the title favourites.

"At this point I think everyone can beat everyone. It's exciting for women's tennis. It's very exciting for us.

"But I still think players like Justine (Henin) and (Amelie) Mauresmo are the favourites."

Joining Ivanovic in the next round will be fifth seed Svetlana Kuznetsova who was given another tough workout by Bethanie Mattek before emerging a 7-6 (7/2) 6-4 winner.

Meanwhile eighth seed Anna Chakvetadze overcame Tatiana Poutchek 6-2 6-1 in just 56 minutes on Court 14.

Other seeds to progress on Thursday included Nadia Petrova (11), Elena Dementieva (12) , Nicole Vaidisova (14) and Patty Schnyder (15), who came from a set behind to defeat Roberta Vinci 2-6 6-3 6-2.

There was also a tough workout for crowd favourite Daniela Hantuchova.

Seeded 10th this year, the Slovakian saw off Russian veteran Elena Likhovtseva 7-5 7-6 (7/3).

Akiko Morigami caused the big upset in the ladies' draw so far when she beat the 13th seed Dinara Safina.

Morigami won a closely-contested second-round encounter 6-4 7-5, Safina becoming the first top-16 seed to exit this year's tournament.

Morigami next plays Venus Williams.

Several of the lower-ranked seeds also bowed out.

Austrian Tamira Paszek claimed the scalp of 17th seed Tatiana Golovin, beating the Russian-born Frenchwoman 6-2 3-6 6-1.

Tathiana Garbin (21) and Francesca Schiavone (29) also crashed out to Victoria Azarenka and Aravane Rezai respectively.