Julian Fellowes's hit period drama drew an average of 8.14m (30.7%) in the 9pm hour, thrashing Andrew Marr's History of Modern Britain which settled for 3.31m (12.4%) on BBC One.
However, Downton's audience - boosted by 284k (1.6%) watching on ITV1 +1 - was nevertheless 1m lower than the equivalent episode last autumn and 600k short of last week's premiere rating.
The X Factor's unveiling of the Final 24 acts categories logged 8.86m (33.6%) between 7.30pm and 9pm (+1: 402k/1.5%), shedding 400k week-on-week despite a guest appearance from Simon Cowell.
Despite the drop, The X Factor was the most-watched broadcast of the day, and its ITV2 spinoff show The Xtra Factor attracted 1.01m (3.8%) at 9pm (+1: 152k/0.8%).
BBC One's Countryfile maintained a solid 5.63m (20.6%) in the 8pm slot, prior to which Fake or Fortune? interested 4.29m (17.9%). Match of the Day 2 netted 2.68m (21.1%) later on from 10.30pm.
Channel 4's Big Fat Quiz continued to prove popular, as the 90s leg pulled in 2.67m (11%) from 9pm until 10.30pm, appealing to a further 340k (2.2%) on +1. Kevin McCloud's Man Made Home opened with 2.6m (9.5%) an hour earlier, adding 347k (1.3%) on timeshift.
Over on BBC Two, Dragons' Den took 2m (7.5%) in the 9pm hour, while Channel 5's best audience of the day came in the early evening for family movie Monsters Inc, which entertained 2.05m (10.1%) and 283k (1.3%) on +1.
Overall, ITV1 claimed a convincing primetime win with 25.6% over BBC One's 17.8%. Channel 4 earned third place with 8.9% (+1: 0.9%), ahead of BBC Two's 5.4%, and Channel 5's 3.2% (+1: 0.5%).
On the multichannels, Family Guy amused 824k (3.8%) at 10pm on BBC Three, while Sky Sports 1's coverage of Liverpool v Manchester United averaged an impressive 1.99m (13.5%) between 1pm and 3.30pm.
BARB ratings data supplied by Attentional