'Mistresses' is a modern take on the lives of four thirty-something women, played by Sarah Parish, Orla Brady, Sharon Small and Shelley Conn, and their involvement in an array of illicit and complex relationships.
It pulled in an average audience share of 19.6% from 9pm to 10pm, 1% more than the 18.6% share achieved by ITV1's detective drama 'Taggart'.
'Taggart' was watched by 4.4m viewers in between 9pm and 10.30pm.
Five launched the new series of US crime drama 'CSI: Crime Scene Investigation' last night, which pulled in 3.5m UK viewers and an average audience share of 14% from 9pm to 10pm.
The second instalment of 'Hugh's Chicken Run', Hugh Fearnley-Whittingstall's three-part contribution to Channel 4's 'Big Food Fight' series, fell just short of the number of viewers it recorded on Monday night.
It drew in 3.3m viewers, an audience share of 13.2%, between 9pm and 10pm -- a steady performance when compared to the 3.4m viewers attained the night before.
The programme concludes tonight, but Jamie Oliver will continue the series on Friday night with 'Jamie's Fowl Dinners'.
BBC Two rounded off the 9pm timeslot with 'This World - The Boys from Bagdhad High', which attracted around 645,000 viewers or an audience share of 2.6% from 9pm to 10.30pm.
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