With Jimmy Carr, James Corden and Lorraine Kelly guest-starring, the format - adapted from the US - appealed to 1.73m (8.4%) from 9pm, down a disappointing 700k week-on-week.
The Marriage Ref's performance is ITV1's worst on a Saturday night since The Prisoner last spring.
Topping the night with just 4.94m (23.8%) was BBC One's Casualty for an episode titled 'Rogue', which saw Dr Adam Trueman struggle to deal with a patient sex-offender, while Lee Mack's All Star Cast amused 3.16m (16.5%).
Elsewhere on ITV1, 3.05m (21.1%) watched You've Been Framed at 6.45pm (+1: 134k), then Bradley Walsh's Odd One In entertained 3.2m (20%) at 7.15pm ahead of Total Wipeout's 2.96m (18.2%) for BBC One, before Penn and Teller: Fool Us gripped 2.88m (15.3%) from 8pm (+1: 294k).
Channel 4's screening of Sister Act fetched 1.21m (7.9%) from 7pm (+1: 139k), after which the latest Camelot averaged 1.18m (5.7%) at 9pm (+1: 142k).
Meanwhile, CSI: NY (8pm), CSI (9pm) and Law & Order: SVU (10pm) held respective audiences of 824k (4.5%), 875k (4.3%) and 1.29m (6.9%) on Channel 5.
Over on BBC Two, Have I Got a Bit More News For You interested 1.91m (9.2%) at 9pm, and The Secrets of the Pop Song took 1.05m (6.6%) at 9.45pm.
Overall, BBC One led primetime with 20.1%, ahead of ITV1's 12.9% (+1: 0.8%), Channel 4's 6.1% (+1: 0.8%), BBC Two's 5.8%, and Channel 5's 4.9%.
BARB ratings data supplied by Attentional