Previously, the 10-part series opened to 1.92m (11.5%) on Sunday, June 14, while last week's episode managed 1.69m (9.2%).
Earlier on Channel 4, Celebrity Wife Swap had 1.91m (8.8%) at 8pm, then 1.88m (8%) stayed with the channel for the Big Brother highlights show.
The second episode of BBC One's Jam & Jerusalem, which stars Dawn French and Jennifer Saunders, logged 3.45m (15.8%) during the 8pm hour. The audience then rose to 5.29m (22.5%) for Rivers With Griff Rhys Jones at 9pm.
BBC Two's live coverage of the Athletics World Championships averaged 3.31m (18.6%) between 5pm and 9pm, then a Top Gear repeat took 2.91m (12.4%).
The final instalment of ITV1's Single-Handed was seen by 3.17m (15%) at 9pm. Earlier, 2.88m (14.2%) tuned in for the two-hour Poirot at 7pm.
Five's film-fest kicked off with Mr Nice Guy, which had 839k (3.7%) between 8.05pm and 10pm. Hard To Kill, starring Steven Seagal, then averaged 1.24m (8.2%) between 10pm and 11.50pm.
Overall, BBC One came top during primetime with an average share of 18.6% to BBC Two's 16.6%. ITV1 was third with 14.6%, followed by Channel 4 with 6.7% (+1: 0.8%) and Five's 4.4%.
BARB ratings data supplied by Attentional