NBC’s “Must See TV” lineup on Thursday proved the most dominating primetime night to date for the May sweeps, delivering overnight numbers of a 21.3 rating/32 share in households in the 37 metered markets — the net’s highest-rated Thursday since Feb. 20.

Leading the charge was a 26.3/39 for “ER” (its highest overnight figures in nearly three months) and a 23.4/34 for the 150th episode of “Seinfeld.” Several ticks back were “Fired Up” (18.1/26), “Friends” (17.8/28) and “Suddenly Susan” (16.3/25).

Sweeps also held to form on Friday and Saturday nights.

Clark interview boosts ’20/20′

ABC took Friday in households with a 9.7/18 average in “fast national” preliminary numbers to NBC’s 8.5/16, CBS’ 7.5/14 and Fox’s 5.4/10. NBC won the race from 8 to 10 but got trounced by ABC’s “20/20″ at 10 p.m. (13.5/24, up from its season-to-date 12.8/23 in overnights).

The latter received a boost from Barbara Walters’ interview with O.J. Simpson prosecutor Marcia Clark, who is just starting to make the book-plugging rounds.

On Saturday, meanwhile, CBS retained its season-long edge in prime with “fast national” figures of 9.8/19 in households with a lineup of “Dr. Quinn, Medicine Woman” at 8, “Touched By An Angel” at 9 and “Walker, Texas Ranger” at 10.

NBC was a distant second in households on Saturday with a 7.1/14, with Fox nosing out ABC for third place, 5.6/11 to 4.6/9.

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