The live cricket coverage on Channel 4 peaked at 7.4m at 6.15pm as England claimed a 2-1 victory for the Ashes.
Channel 4's viewing figures grew steadily throughout the day, hitting 6.2m at 5pm and not dropping below 6m until 6.45pm.
The record viewing figures will renew calls for live cricket matches to remain on terrestrial television.
Earlier this year, BSkyB won the TV cricket rights with a £220m deal after outbidding terrestrial rivals, Channel 4 and the BBC. The resulting deal means that live cricket will not being shown on terrestrial TV from 2006.
Five managed to claim the highlights package for Test matches after it outbid Channel 4, which bid jointly with Sky.
Under the Broadcasting Act 1998, highlights of Group B listed events, such as cricket, must be offered to broadcasters on a channel that reaches 95% of the population.
Broadcasters were free to lodge a complaint to Ofcom about Sky's exclusive package and Five's highlights deal, because Five does not have full national free-to-air coverage across the UK, giving it less than the 95% that is required by the act.
However, Ofcom did not uphold any complaint. If it had, the deal could have been scuppered.
It is now up to the Department of Culture, Media & Sport to intervene on cricket TV rights, because it decided to put cricket in the Group B list of events in 1998.
There has been speculation that the Ashes or Test matches could be nominated as a "crown jewel sporting event", along with the Olympics and World Cup among others, by culture secretary Tessa Jowell ensuring it a place on terrestrial TV in future.
The second-highest Channel 4 viewing figure this year was for 'Big Brother''s Friday night finale in August, which brought an average 6.7m to Channel 4.
That marked one of the best weeks in the channel's history, with US import 'Lost' securing 6m viewers on its debut night on Wednesday night.
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