Theroux's latest documentary strand - Extreme Love - ended with 1.97m (8.6%) at 9pm on BBC Two and BBC HD, a tad higher than last week's opener.
However, the audience is down on the 3m that watched Miami Mega Jail last May.
After Theroux, Grandma's House took 754k (4.2%) at 10pm, while 8pm's Two Greedy Italians interested 1.44m (6.2%).
With help from ITV's 8pm soap hour, Long Lost Family continued to perform well with 4.52m (19.7%) at 9pm, adding 303k (1.7%) on ITV1 +1. Current affairs show Tonight logged 3.17m (14.6%) at 7.30pm (+1: 125k/0.5%).
Over on BBC One, 4.16m (17.8%) watched Watchdog at 8pm, then a New Tricks repeat nabbed 4.14m (17.9%), and 10.35pm's Question Time took 2.77m (21.8%).
Football coverage helped Channel 5 edge Channel 4 as a Europa League semi-final clash scored 1.29m (5.6%) between 8pm and 10.15pm, while 1.19m (5.4%) watched 4's The Plot To Bring Down Britain's Planes from 9pm (+1: 214k/1.4%).
Overall, ITV1 led primetime with 21.9% (+1: 0.9%), slightly pulling ahead of BBC One which averaged 21.1%. BBC Two was third with 6.5%, followed by Channel 5's 4.6% (+1: 0.1%), and Channel 4's 4.5% (+1: 0.8%).
BARB ratings data supplied by Attentional