Clarke was fired after his team lost a task selling baby accessories at a trade show in London's Earl's Court.
Sir Alan Sugar said he initially saw a "bright light" of potential in Clarke, but the spark had "gone out". The programme attracted a 34.7% share of the 9pm-10pm audience.
ITV1's 'Midsomer Murders' came in second in the ratings battle, lagging behind with 3.6m viewers and a 15.9% share of the 8pm-10pm audience.
Last night's instalment of the long-running drama, starring John Nettles, saw detectives investigating the deaths of two members of a recently reformed rock band.
A repeat of Channel 4's 'Grand Designs' series, following householders on a mission to redesign their homes, won 2m viewers and an 8.2% share of the 9pm-10pm audience. Including Channel 4+1 figures it reached 2.2m viewers.
Five's documentary 'Extraordinary People: Electric Human', featuring a man who can withstand high-voltage currents without any apparent ill effects, powering light bulbs and firing sparks from his fingers, netted 1m viewers and a 4.2% share of the audience.
'Why Poetry Matters', the official introduction to the BBC's poetry season presented by Griff Rhys Jones, drew 774,000 viewers and a 3.1% share of the audience to BBC Two.
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