An average of 8.9 million people watched the opening episode, which saw the return of Cheryl Fernandez-Versini and Simon Cowell to the judging panel.
This was up slightly on the 8.8 million who watched last year's launch episode.
Former Spice Girl Mel B made her debut as a judge, having filled the same role on the Australian version.
A further 400,000 people watched on the ITV+1 channel.
The second most watched programme of the night was Doctor Who on BBC One, which had an average of 5.2 million viewers. This was down more than two million on last week's episode, which was Peter Capaldi's full debut in the title role.
Simon Cowell returned to chair the X Factor judges, taking over from Gary Barlow, having launched the show back in 2004. He quit being in front of the camera in the UK in 2010 to spearhead X Factor USA, which ran for three seasons until it was axed this year.
The return of BBC One's Strictly Come Dancing on Saturday will see the two Saturday night big hitters go up against each other after several years of avoiding such a clash.
Strictly will go out from 20:00-21:15, while X Factor airs from 20:00-21:05.
The BBC said the overlap was unavoidable because it had scheduled Strictly to avoid clashing with an extra edition of Coronation Street.
Cowell criticised the BBC's decision, saying it would only hurt the viewers.
He said: "They say this isn't a ratings battle, it is, that's why they did it. They didn't have to put it on at the same time as us, they did and it means that people then have to make the choice where before I think it was more of a gentlemen's type agreement but it just shows as far as I'm concerned, this is personally speaking, the producers of the show for what they are.
"They don't want this show to do well, they don't want people to watch it, and our job is to do the best job we can so people prefer X Factor to them."
Correction 8 September 2014: This story has been amended to clarify the number of people watching The X Factor as it was broadcast and adds the number watching on the ITV+1 channel.
X Factor's return saw it dominate Saturday night's television, with 40% of the viewing public tuning into its launch episode on ITV.