The first episode of Downton Abbey's fifth series was watched by an average audience of 8.1m on Sunday evening.
It beat the debut episode of five-part BBC One army drama Our Girl, which attracted an average audience of 3.9m.
An extra 300,000 watched Downton on ITV's +1 channel. But it was just over a million less than the 9.2m who saw the first episode of series four.
The latest instalment of Julian Fellowes's period drama attracted a mixture of reviews.
Andrew Billen, writing in The Times, gave Sunday's episode four stars in his review.
"Lord Fellowes, who may yet get through a series without resorting to murder, rape or sudden death, is filling his plots very enjoyably with sex instead," he said.
The Telegraph's Ben Lawrence concluded "there are still faults with Downton Abbey".
"Some of the dialogue should really have been left on the cutting room floor - 'Tom, come with me. You know where the sandbags are kept!' Also, the large ensemble is beginning to feel unwieldy.
"But it is such an enjoyable confection that these criticisms feel niggardly."
The Independent's Ellen E Jones described the episode as "slow-moving", but said that Dame Maggie Smith's portrayal of the Dowager Countess was worth seeing on its own.
"If this slow-moving series eventually unravels (as I think it must) into only the Dowager's decrepit form, alone at Dower House, whispering cutting asides into the fire, we will be none the worse off for it," she wrote.
The new season of Downton is set in 1924, as Britain's first Labour government comes to power.
New actors to join the series include Richard E Grant, who joins the cast as Simon Bricker, one of the guests of the Grantham family.
Anna Chancellor also joins in a guest role, playing Lady Anstruther, while 24 actor Rade Sherbedgia plays a Russian refugee.
Downton Abbey has also become a cult hit in the US, and more than 100 countries have broadcast rights.