The first presidential debate of the fall garnered an average of 52.4 million viewers on Friday, Nielsen Media Research said on Monday.

The relatively low audience estimate puzzled some television executives who expected a wider audience for the commercial-free forum between John McCain and Barack Obama. The debate drew 8 million fewer viewers than the first debate between George W. Bush and John Kerry in 2004 — but attracted 6 million more viewers than the second debate that year, which was similarly held on a Friday.

Of the 11 broadcast and cable channels that telecast the McCain-Obama debate, ABC reached the most viewers, with an average of 11 million watching. Among other broadcasters, CBS had an average of 7.6 million and NBC had an average of 7.1 million. On cable, an average of 8.2 million watched the Fox News Channel, 7.1 million watched CNN and 3.9 million watched MSNBC.

Nielsen’s measurement of the home audience does not include out-of-home viewing parties, television repeats or Internet streams of the debate. C-SPAN’s video of the debate has elicited more than half a million views on YouTube.

From the NYTIMES.