The first episode of the series, which is fronted by Cat Deeley and features Nigel Lythgoe and Arlene Phillips as judges, charted the audition phase and boot camp stage.
Overall, the 75-minute episode averaged 6.44m (27.4%), but more crucially, the audience grew steadily throughout its runtime. At 6pm, just 4.64m (21.1%) were watching but by 7.15pm this had built to 8.07m (33.7%).
> Click here to read our interview with Cat Deeley
Immediately afterwards on BBC One, the second Total Wipeout Celebrity Special appealed to 7.53m (30.1%). A new series of The National Lottery: In It To Win It - fronted by Dale Winton - followed at 8.15pm with 5.81m (22.6%), then a feature-length episode of Casualty put in 6.62m (26.8%) between 9.05pm and 10.55pm.
Live coverage of the FA Cup third round game between Reading and Liverpool averaged 5.09m (23.1%) for ITV1 between 5pm and 7.15pm, peaking with 6.79m (28%) at 7pm.
New dating show Take Me Out launched to 3.62m (14.4%) at 7.15pm, then an hour later, the latest edition of All Star Mr & Mrs logged 4.18m (16.2%). Piers Morgan on Las Vegas, featuring interviews with Paris Hilton and Sylvester Stallone, interested 3.34m (13.3%) from 9.20pm.
BBC Two's Elvis week began at 8pm last night with documentary Elvis By The Presleys, seen by 2.35m (9.1%) over 90 minutes. Elvis: Black Leather - The '68 Comeback Special then drew 1.71m (6.9%) between 9.30pm and 10.20pm.
Channel 4's screenings of Night At The Museum, Bury My Heart At Wounded Knee and The Cider House Rules gathered audiences of 2.56m (10.2%), 1.16m (5.2%) and 357k (5%) respectively.
As usual, US reruns occupied Five's Saturday night schedule, starting with 1.08m (4.2%) for NCIS at 8pm. CSI: NY had 1.18m (4.6%) at 9pm, after which CSI drew 958k (4.1%) and Law & Order: SVU drew 923k (5.8%).
Overall, BBC One had a comfortable primetime victory with an average share of 26.7% to ITV1's 15%. Channel 4 was third with 7.7% (+1: 0.8%), followed by BBC Two with 7.7% and Five with 4.1%.
Meanwhile, ITV3 dominated the multichannel ratings last night, led by a classic episode of A Touch Of Frost, which averaged 968k (4%) from 9pm. Earlier, episodes of Marple and Rosemary & Thyme picked up 795k (3.4%) and 748k (2.9%) respectively.
Also popular was BBC Three's screening of War Of The Worlds, seen by 949k (3.9%) from 9.05pm.
BARB ratings data supplied by Attentional