The show, which saw 16 contestants enter the new Big Brother house only to learn they weren't real housemates, attracted 4.79m (22.1%) to Channel 4 between 9pm and 10.30pm.
A further 293k (1.9%) tuned in on Channel 4+1, while 512k (3.9%) watched Davina McCall present Big Brother's Big Mouth on E4 at 10.30pm.
Last year, 5.31m (24.5%) tuned in for the Big Brother 9 live launch on June 5, 2008, equating to a ratings fall of around 9.4% year on year. The most-watched live launch show was Big Brother 5, which put in 7.23m on May 28, 2004.
Despite the figures being down this year, Big Brother managed to comfortably win its timeslot. Its nearest rival, ITV1's Taggart, was seen by 3.27m (14.8%) at 9pm.
Calendar Girls: Ten Years On, which saw six of the original girls bare all once more, took 2.99m (13.6%) for BBC One, Five's The Mentalist put in a solid 2.45m (11.1%), while A World Of Pain: Meera Syal On Self-Harm drew 1m (4.5%) for BBC Two.
BBC One's Traffic Cops won the 8pm hour, pulling in 4.24m (20.9%), The Bill managed 3.9m (19.2%) for ITV1 and BBC Two's Springwatch interested 3.31m (16.3%).
Over on Channel 4, 1.66m (6.2%) tuned in for the third episode of The Home Show. Five came last for the hour, drawing 457k (2.3%) with a repeat of Paul Merton In India.
Overall, BBC One came top during primetime with an average share of 22.1% to ITV1's 16.8%. Channel 4 was third with 13.8% (+1: 0.8%), followed by BBC Two with 8.1% and Five's 5.2%.
Elsewhere, a new season of America's Got Talent launched well for ITV2, pulling in an impressive 1m (5.5%) during the 8pm hour and then 531k (3.1%) at 10pm. Also on the channel, 867k (4.3%) tuned in for Katie & Peter: Stateside at 9pm, a drop of 573k from the previous episode, which aired two weeks ago.
Ratings data supplied by Attentional