Only 3.46m (15.8%) watched the likes of Frankie Cocozza, Natalie Cassidy and Kirk Norcross enter the house from 9pm, a significant fall of 1.7m on last summer's series.
However, viewers stuck around for Celebrity Big Brother's Bit on the Side presented by Emma Willis, which won its 11pm timeslot with 1.07m (10.4%).
ITV1's Eternal Law edged BBC One's Public Enemies in the 9pm drama battle with 4.32m (17.3%) against the latter's 4.14m (16.6%). Eternal Law also pulled in 360k (1.9%) on ITV1 +1.
Over on BBC Two, Meet Britain's Chinese Tiger Mums interested 1.06m (4.2%), while Restoration Man logged 2.06m (8.3%) for Channel 4 (+1: 208k/1.1%).
During the 8pm hour, BBC One's nature series Earthflight continued with 4.63m (17.8%), holding up well against ITV's soap double of Emmerdale and Corrie.
Meanwhile, Location, Location, Location took 2.19m (8.5%) for Channel 4 (+1: 264k/1.1%), while 1.07m (4.1%) watched Channel 5's Building the Ice Hotel, and a Top Gear repeat had 1.59m (6.3%) between 7.30pm and 9pm.
George Lamb gameshow The Bank Job slumped to 1.03m (5.5%) at 10pm, adding 128k (1.3%) on Channel 4 +1.
Overall, ITV1 led primetime with 21.9% (+1: 0.9%) against BBC One's 20.4%. Channel 5 soared to third place with 9%, beating Channel 4's 6.5% (+1: 0.8%) and BBC Two's 5.3%.
BARB ratings data supplied by Attentional