The show captured a massive 48% share of the audience in its 7.30-8.30pm slot, as the Girls Aloud singer joined fellow judges Simon Cowell, Louis Walsh and Dannii Minogue.
At its peak, the programme attracted 12.1m viewers and a 54% share of the audience. The first episode of last year's series drew an average audience of 9.5m viewers, with the finale - which saw Leon Jackson win - gaining an audience of 12m.
In the opening instalment of the talent search series, Cole was seen leaving the set when a friend from 'Popstars: The Rivals' auditioned, saying it would be "biased".
Cole was a contestant on the show in 2002 and was chosen to become a member of pop group Girls Aloud.
BBC One's national lottery show 'The National Lottery: This Time Tomorrow' was watched by 3.6m viewers and a 17% share between 7.30pm and 8pm.
'The X Factor' was also up against the first 30 minutes of BBC One's 'The Inspector Lynley Mysteries', which had 3.9m viewers and an 18% share of the audience between 8.20pm and 8.50pm.
BBC Two's 'BBC Proms 2008: Great Conductors' earned a lowly 700,000 viewers and a 4% share of the audience between 7pm and 8.30-pm, while movie spin off 'Porridge' brought Channel 4 1.5m viewers and a 7% share between 7.15pm and 9pm.
Five's 'Superstars' netted just 300,000 viewers and a 2% share of the audience between 7.05pm and 7.55pm.
Earlier in the day, BBC One's Olympic coverage was watched by 4.5m viewers and a 47.7% share between 8.15am to 4.30pm.
Increased interest after Team GB's storming performance in swimming, cycling and sailing is likely to have boosted Sunday's ratings. In the same daytime slot, BBC One's coverage was watched by 4.9m viewers and a 46.8% share.
The same channel's 7-8pm Olympic highlights package drew 4m viewers but this was just a 19.2% share as ITV1's evening schedule exerted its pull.
'Heartbeat' won the 7-8pm slot with 6.4m viewers and a 31.1% share, which was followed by a two-hour long episode of 'Midsomer Murders', with 6.6m and a 27.1% share.
BBC One's wildlife documentary 'Pacific Abyss' watched by 3.9m and a 16.4% share.
At 8-9pm the second of its three-part 'Britain From Above' documentary series dropped to 4.5m viewers, a share of 18.1%, from 5.2m last week.
Five enjoyed a strong showing for its terrestrial premiere of comic book adaptation 'Hellboy', coinciding with the cinema release of the sequel.
Running at 8-10.15pm 'Hellboy' earned 2.8m viewers and a 11.7% share for Five, which was higher than BBC Two's 1.9m for a repeat of 'Top Gear'.
Ratings for 'Big Brother' continue to hold up after ten weeks, with 3.5m tuning in on Friday night to see Stuart lose the eviction vote, or 3.6m if ratings for Channel 4+1 are included.
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