“Matlock,” in its debut on ABC, made a convincing motion for a series slot last week, combining with the second-best “PrimeTime Live” rating ever to give the alphabet network its first regular-season, Thursday-night victory in nearly seven years.A two-hour “Matlock” ranked first in terms of households from 8-10 p.m. with a 14.8 rating, 22 share, siphoning away audience from CBS’ “Top Cops” and “Street Stories.” According to ABC research, the last time the web won a Thursday during the season was with “20/20″ and the miniseries “North and South” on Nov. 7, 1985. The bulk of the “Matlock” audience was comprised, as usual, of older viewers (a 40 share of women over 50), and its 14 share among adults 18-49–the primary sales demographic–ranked third, although it was still comparable with the performance of regular occupants like “Delta” and “Homefront.” “PrimeTime,” featuring a Magic Johnson interview, then won the 10 p.m. hour with a 17.0/28, its best results since interviewing William Kennedy Smith rape accuser Patricia Bowman. ABC has a 22-episode order on the venerable Viacom Prods. hour but hasn’t decided on a time period for it yet. The show could end up on Saturday, where the web has blown out its 8-10 p.m. block in favor of “Columbo” movies until January (Daily Variety, Nov. 6).