The medical drama, celebrating its 25th year on air this September, pulled in 5.47m (25.4%) from 9pm for an episode titled 'Pascal's Wager'.
Head-to-head with ITV's flagship summer entertainment show, Penn & Teller: Fool Us, hosted by Jonathan Ross, took 2.96m (13.9%). However, the magician double-act appealed to 241k on ITV1 +1.
Despite the low figure, Penn and Teller was ITV's most popular primetime offering. Harry Potter and the Deathly Hallows: Behind The Magic interested 2.87m (14.2%) at 7.15pm (+1: 464k), Odd One In entertained 2.32m (11.1%) at 8.15pm (+1: 233k), and The Marriage Ref slumped even further to 1.51m (8.6%) at the later time of 10pm.
Meanwhile, John Barrowman vehicle Tonight's The Night continued to dazzle 4.53m (22.4%) at 7.10pm, The National Lottery: In It To Win It quizzed 5.35m (25.7%) at 8.10pm, and the fifth episode of Lee Mack's All Star Cast amused 3.4m (17.8%) at 9.50pm.
Over on BBC Two, classic Dad's Army drew 2.04m (10%) at 7.30pm, after which 1.17m (5.6%) watched The Impressionists: Painting and Revolution in the 8pm hour. Have I Got A Bit More News For You followed at 9pm with 1.65m (7.7%), and Secrets of the Pop Song mustered 854k (4.5%).
Channel 4's screening of Marley & Me managed 1.41m (7%) between 6.55pm and 9pm (+1: 215k), then 1.1m (5.2%) tuned in for Camelot (+1: 121k).
Elsewhere, NCIS (7.05pm), Law and Order (8pm), CSI (9pm) and Law & Order: SVU (9.50pm) secured respective audiences of 787k (3.9%), 848k (4.1%), 969k (4.5%) and 1.32m (7.1%).
Overall, BBC One stormed primetime with 22.5%, ahead of ITV1's 12.9% (+1: 2.2%), BBC Two's 7%, Channel 4's 6% (+1: 0.8%), and Channel 5's 4.8%.
BARB ratings data supplied by Attentional