Morning Ratings Flash - Rick Kissell

Shaking things up on the opening night of the February sweep, ABC enjoyed its strongest Thursday in two years thanks to its 30th anniversary “Happy Days” special, according to preliminary nationals from Nielsen.

While NBC led the night in adults 18-49 and CBS in total viewers, the two-hour “Happy Days Reunion” racked up big numbers for ABC (6.3/15 in adults 18-49, 19.9 million viewers overall), tying for the adults 18-49 lead from 8 to 10 and leading in other ratings categories. The Alphabet delivered its strongest non-sports ratings on a Thursday since the night of the Michael Jackson documentary in February 2003.

ABC’s strong perf seemed to affect some other shows, with NBC comedy “Joey” (4.3/12 in adults 18-49, 10.0 million viewers overall) delivering its second lowest-rated numbers for an original episode, and CBS drama “CSI” (8.9/21 in adults 18-49, 24.8 million viewers overall) falling to a firstrun season low. Still, “CSI” led its hour across the board and stands as the night’s top-rated program.

NBC’s “The Apprentice” held up pretty well at 9 (7.2/17 in adults 18-49, 14.9 million viewers overall) as did Fox’s “The OC” at 8 (3.4/9 in adults 18-49, 7.2 million viewers overall).

At 10, NBC’s “ER” (8.8/22 in adults 18-49, 18.1 million viewers overall) was the clear choice in all categories except total viewers, which went to CBS drama “Without a Trace” (6.0/15 in adults 18-49, 19.3 million viewers overall). Thanks to a stronger lead-in, ABC was a bit more competitive with newsmag “Primetime” (3.1/8 in adults 18-49, 9.0 million viewers overall).

Preliminary adults 18-49 averages for the night: NBC, 6.9/17; CBS, 6.2/15; ABC, 5.2/13; Fox, 2.5/6; UPN, 1.6/4; WB, 0.8/2.

In total viewers: CBS, 18.5 million; ABC, 16.3 million; NBC, 14.3 million; Fox, 5.3 million; UPN, 4.5 million; WB, 2.5 million.

Follow @Variety on Twitter for breaking news, reviews and more