CNN suffered its worst ratings among primetime viewers in the most coveted demographic by advertisers — dealing a gut punch to embattled new boss Mark Thompson.

The cable channel, which touts itself as “the most trusted name in news,” drew just 83,000 viewers aged 25 to 54 during the week of May 13-19 from 8 to 11 p.m. — its lowest-rated week since 1991, according to Nielsen.

By contrast, Fox News garnered more than the twice the audience in the key demo, with 186,000 viewers, according to Nielsen. Left-leaning MSNBC was a distant second with 111,000, the data showed. ...

Its total viewership for the week was also paltry with 494,000, compared with 2 million for Fox News — which shares common ownership with News Corp, the publisher of The Post. MSNBC pulled in 1.1 million, according to Nielsen.