The first episode of the five-part third series of the Doctor Who spinoff - starring John Barrowman and Eve Myles - pulled in 5.94m (25.8%) during the 9pm hour, coming first place in its timeslot.
Previously, series one opened to 2.4m (12.7%) on BBC Three on October 22, 2006, while 3.72m (14.8%) tuned in for the series two premiere on BBC Two on January 16, 2008.
Torchwood's nearest rival last night was an episode of ITV1's Real Crimelooking at the murder of teenager Hannah Foster. It managed 4.15m (18%) in the 9pm hour, while BBC Two's The Supersizers Eat... The French Revolution had 1.55m (6.7%).
A new series of Alex Polizzi's The Hotel Inspector took 1.57m (6.8%) for Five, and the second part of Channel 4's Inside Nature's Giants series, in which a 60-ton whale was dissected, interested 1.72m (7.5%).
Earlier, at 8pm, Fifth Gear put in 875k (4%) for Five, and Channel 4's Teenagers Fighting Cancer was seen by 830k (3.8%).
Over on BBC Two, University Challenge grabbed 2.43m (11.3%) at 8pm. The audience then fell to 1.71m (7.8%) during the 8.30pm screening of What To Eat Now.
ITV1's half-hour Airline averaged 2.99m (13.9%) at 8pm, and 2.79m (12.7%) watched BBC One's Panorama between 8.30pm and 9pm.
Channel 4's Big Brother highlights show, which featured another argument between Rodrigo and Charlie, managed 1.75m (10.4%) during the 10pm hour.
Overall, ITV1 came top during primetime with an average share of 24.3% to BBC One's 22.7%. BBC Two was third with 6.9%, followed by Channel 4 with 6.2% (+1: 0.7%) and Five's 5.1%.
Elsewhere, One Tree Hill's return to E4 logged 384k (1.8%) at 9pm, beating the first part of Dawn Porter's documentary My Breasts Could Kill Me, which put in 181k (0.9%) for Sky1.
Also at 9pm, the first part of Living's new series, Four Weddings attracted 341k (1.6%).
BARB ratings data supplied by Attentional