Thousands of people around the country were hunched over their keyboards today as the second chance to buy Olympic tickets got under way at 6am.
Organisers said the website was working despite many people experiencing problems throughout the process.
Hopeful fans received error messages as they tried to secure precious tickets for next year's Games, with some being told to 'try again later' even after submitting their payment details.
They were warned not to refresh their browser if they were greeted with a message about "high demand" while applying.
A statement on the London 2012 website said: "Demand is extremely high at the moment on the ticketing website but the system is still transacting.
"If you've clicked submit, don't hit refresh. Please wait and the system will process your order.
"If you receive the error 'sorry, we cannot process your payment details', your tickets will be saved in your basket. Please wait a few minutes and try again."
It added that a range of sports were still available, including football, judo, boxing and volleyball.
Some fans went to Twitter to voice their anger at being unable to secure a seat at the Olympics.
"Inefficient ticket application system for overpriced tickets while corporates cream off the best. This is truly the British Olympics," wrote spursblogger, while JadeEwenFan complained there was "Not 1 Ticket available for Olympics! I tried everything!".
Jacqueline Burke, who was hoping to buy tickets for her family, experienced frustration with the website this morning.
She told BBC Breakfast: "We thought we were doing really well at 6 o'clock because we were able to pick the three events we wanted. But unfortunately having pressed 'submit to pay' it's come back as 'Sorry, we are unable to process your application'."
However, Ms Burke's application was later reported to have been submitted successfully.
Another pleased fan, Emily Hughes, managed to submit an application for two sets of tickets to watch synchronised swimming.
Miss Hughes, 37, said: "I managed to get the application through in about 40 minutes. At every stage it said the session hadn't been processed or had timed out, but I kept going back and doing it again and it eventually went through. I'm thrilled."
Sports fans who missed out in the initial round of tickets have a 10-day first come, first served opportunity to buy 2.3 million unsold tickets.
The second opportunity comes as a British Olympian branded the ticket system "a bit of a shambles".
Three-times Olympic cycle champion Bradley Wiggins, 31, who is hoping to defend his team pursuit title next year, was one of the 1.2 million people who missed out on tickets in the first round ballot.
Many of his family will miss out on seeing him compete at a home Games, he said.
"I think, as most of the public feels, it's a bit of a shambles, the ticket allocation," he told BBC Sport.
"It's a shame when you know what works so successfully in other Olympic Games, certainly Athens, that they couldn't implement those ticket systems here.
"I'd love to have my family there. I grew up in London and would love to have my mum and everyone there watching me but, you know, that's the way it is I suppose, you just get on with it.
"It's a shame but there's nothing you can do about it."
Organisers have guaranteed athletes will be able to buy two tickets for every session in which they are competing.
London 2012 was flooded with 22 million requests from 1.9 million people for the 6.6 million tickets available to the public. So far three million tickets have been sold.
The second chance sale includes tickets for 310 sessions, including 44 medal events - but 1.7 million of the tickets are for the football competitions.
There have been sell-outs for 21 events including the ceremonies, diving, swimming and tennis.
Anyone who got tickets in the first round sale will get another chance to buy from 6am on July 8 to 6pm on July 17.