The two shows were neck and neck on 7.3 million viewers when overnight figures were issued last week, but "consolidated" figures – which include catch-up viewing – show the BBC1 drama ahead by half a million viewers.
It drew 10.15 million viewers for its December 25 special, while ITV1's Downton had 9.6 million, including viewers watching later on the ITV+1 channel.
Downton was the big winner based on consolidated figures a year ago, which meant that, after time-shift viewing was included, it was the biggest Christmas Day show.
However, its seasonal edition screened last week – in which Dan Stevens' character Matthew Crawley was killed off – was the sixth most popular show of Christmas Day.
EastEnders retained its position as the most popular show of December, while Midwife was second.
The Royle Family festive comedy pulled in 9.87 million, making it the third most popular show of the day. Doctor Who was fourth with an audience share of 9.85 million; Coronation Street fifth; Emmerdale eight; and the Queen's Speech at ninth, attracting 6.46 million viewers.
The BBC News was the 10th most watched show of the day, on 6.14 million viewers.