'ER' pulled in 1.4m viewers and an 8% share of the audience in its 10pm slot, narrowly beating 'Prison Break', which was watched by 1.1m viewers and a 6% share of the audience.
Both US imports are highly valued by advertisers for delivering young, high-earning audiences. 'ER' is still going strong on Channel 4, even though it is currently in its 13th season, while 'Prison Break' is a third of the way into its second season on Five.
Channel 4 also scored a minor ratings hit with a political documentary on Gordon Brown. A 'Dispatches' special called 'Gordon Brown - Fit for Office?' attracted 1m viewers and a 4.3% audience share, in its 8pm slot.
A 'Panorama' documentary on the Church of Scientology, famous for high-profile followers such as Tom Cruise and John Travolta, gave BBC One an unlikely ratings boost, on the back of acres of press coverage.
The programme has been dogged by controversy, amid accusations that the Church of Scientology carried out a campaign of intimidation to obstruct BBC reporter John Sweeney.
In the programme Sweeney is seen losing his temper and shouting at Scientology representative Tommy Davis, after he accused the BBC reporter of giving a critic of the faith an easy ride in an interview.
In the end, 'Panorama' was watched by 4.4m viewers and a 19.1% share of audience in its 8.30pm slot.
The viewing figure was 'Panorama's' biggest audience in its new Monday night slot.