Afnan Iftikhar's exit from the opera talent search, hosted by Amanda Holden, was seen by 2.83m (12.7%) between 9pm and 10.30pm - adding 103k (0.6%) on ITV1 +1.
Monday's audience for Superstar was also worryingly 300k lower than Sunday's (July 15) pre-recorded boot camp edition.
Christopher Eccleston's BBC drama Blackout edged Superstar with just 3m (13%), while Undercover Boss interested 1.96m (8.5%) on Channel 4 (+1: 320k/1.7%), and 1.39m (6%) watched Operation Crossbow on BBC Two.
Airing against EastEnders in the 8pm slot, Britain's Secret Treasures opened with 3.87m (16.8%) on ITV1 (+1: 133k/0.6%), University Challenge returned to BBC Two with 2.02m (8.7%), and Dispatches rallied to 1.2m (5.6%) for Channel 4 (+1: 178k/0.6%).
Meanwhile on Channel 5, Police Interceptors slipped to 907k (3.9%) in the 8pm hour, then 1.29m (5.6%) caught the latest Big Brother highlights show, and The Walking Dead attracted 831k (4.4%).
Amazingly, an old edition of the recently cancelled detective drama Lewis beat Big Brother, drawing 1.38m (6.6%) to ITV3 between 9pm and 11pm.
Overall, ITV1 topped primetime with 21.4% (+1: 0.6%), seeing off BBC One's 17.9%. BBC Two and Channel 4 tied in third place with 5.7% (C4+1: 0.9%), ahead of ITV3's 4.5% and Channel 5's 3.9% (+1: 0.2%).
A BBC Four documentary about the history of toilets, The Toilet: An Unspoken History, sucked in 1m (4.3%) in the 9pm slot.
BARB ratings data supplied by Attentional