An average of 9.84m (38.2%) saw it live on ITV1 with an additional 238k (1.4%) catching the period drama on timeshift.
Downton Abbey was preceded by The X Factor's results show, which grabbed 8.94m (33.2%) and 245k (0.9%) on +1.
Surprise Surprise took 4.11m (16.5%) at 7pm (+1: 269k/1%).
On BBC One, Strictly Come Dancing earned 9.63m (37.4%). Countryfile aired earlier to 7.26m (32%) and Antiques Roadshow had 5.85m (21.7%) from 8pm.
Andrew Marr's History of the World appealed to 2.55m (9.5%) afterwards.
Meanwhile, BBC Two showed Obama: What Happened to Hope? (1.08m/4.1%) and Space Dive (1.43m/5.3%).
Channel 4's Homeland continued with 1.84m (7%) from 9pm (+1: 121k/0.6%), which was followed by Friday Night Dinner (622k/3%). How Britain Worked managed 1.18m (4.4%) in the 8pm timeslot (+1: 189k/0.7%).
Lastly, Channel 5 showed Hancock and Bangkok Dangerous, which drew 1.27m (4.8%) from 7.30pm (+1: 133k/0.5%) and 1.25m (5.3%) from 9pm (+1: 151k/1.1%) respectively.
Overall, ITV1 convincingly won primetime with 29.7% (+1: 0.8%), beating BBC One's 20.7%.
Channel 5 took a surprise third place with 5% (+1: 0.5%), as Channel 4 and BBC Two tied with 4.7%. Channel 4 had an extra 0.6% on +1.
BARB ratings data supplied by Attentional