Some 11.8m - approximately 50% of the viewing audience - were fixed to the running event involving the British duo of Jo Pavey and Julia Bleasdale at 10pm.
Despite setting new personal bests, Pavey and Bleasdale finished seventh and eighth respectively as Tirunesh Dibaba retained her title.
The figures, which combine BBC One and BBC Olympics HD, do not account for crowds watching in pubs and on big screens.
Rebecca Adlington's swimming bronze had a peak audience of 11.3m earlier on in the evening.
BBC One's star-studded evening coverage, featuring the likes of Jessica Ennis, never dropped below 8 million between 6.55pm and 10.05pm.
> London 2012 Olympics: This weekend's must-watch TV guide