The first of David Blaine's 44 days in a perspex box over the Thames drew more than a million viewers to Sky One on Friday.
Blaine will be stuck for 44 days in his Thames prison
Blaine's stunt - where he is encased in a box without food or human contact for 44 days - is being televised on Sky One and Channel 4.
According to unofficial TV overnight figures, Friday's show drew 1.02 million viewers, an 8.5% share in multi-channel homes.
Sunday night's episode, the third night of Blaine's stunt, drew 308,000 viewers.
Channel 4's coverage of the event begins on Monday.
Blaine has been imprisoned in a perspex box measuring 7ft deep, 7ft long and 3ft wide, with no means of communication during his month-and-a-half exile.
He is well-known for his publicity-generating stunts, including standing for days in a block of ice and standing on top of an 80ft pole for more than 36 hours.
He first found fame performing his brand of "street magic" for US television.
The magician said before he started the test of his endurance that he was more concerned about the mental effects than the physical effects.
He said: "I am not worried about the first three weeks of this. I know the first three weeks I can handle; I'm worried about the second half of this when I start to lose my mind and everything becomes really bad."