Toby Whithouse's 'A Town Called Mercy', guest starring Ben Browder, averaged 6.61m (29.1%) for BBC One between 7.35pm and 8.20pm.
Not since April 2010, for an episode featuring the Weeping Angels and the return of River Song, has Who been as popular in the overnight ratings.
Doctor Who's figures are expected to rise even further when viewers who recorded the show and watched later are added to the equation.
As of Monday morning, the sci-fi drama remains BBC iPlayer's 'Most Popular' request.
The programme's series seven premiere managed 6.4m a fortnight ago, while last week's 'Dinosaurs on a Spaceship' could only muster 5.5m.
Doctor Who was given a helping hand from Strictly Come Dancing, which attracted a peak of 9.8 million for its 2012 launch in the 6.30pm slot.
Red or Black was Who's nearest competitor with half the drama's audience. The Simon Cowell gameshow delivered 3.29m (14.9%) to ITV1 between 7.25pm and 8.10pm, returning later in the night with 3.35m (15.4%) from 9.10pm.
BARB ratings data supplied by Attentional