Torchwood: The New World had an average audience of 4.8 million viewers on BBC One and BBC One HD, according to unofficial overnight figures.
The UK premiere of the new series had an 21% share of the audience and was the 5th most watched programme of the day, behind the four main soaps. It won the 9pm timeslot, with Single Handed on ITV1 getting 3.7 million viewers.
Episode One of the last Torchwood series, Children of Earth, had an overnight ratings of 5.9 million and a final figure of 6.47 million viewers.
The final ratings for The New World will be released next week and will include those who record the programme and watch it within seven days.