NBC was on top of the broadcast ratings world Tuesday night, with its two-hour season finale of “The Voice” topping all shows in the Nielsen overnights and leading the network to an overall win for prime time in the key 18-49 demo, TVbytheNumbers.com reports.

But at the other end of the ratings spectrum, ABC’s 10 p.m. drama “Private Practice” took a startling fall, plunging six-tenths of a ratings point from last week’s 2.1 average to an all-time low for the series, a 1.5 rating. And ABC came in last overall among the big 4 broadcast nets.

“The Voice” pulled in a 4.3 average in 18-49, surging from last week’s 3.1 rating and up 16% from the show’s June 2011 season finale. NBC’s average for the night was dragged down by a 1.3 for “Fashion Star,” but the network still easily won the night with its 3.3 average for prime time.

Finishing second behind NBC for prime was CBS with a 2.7 average in 18-49, followed by Fox (2.4) and ABC (1.8).

The story in total viewers was different, as CBS’s “NCIS” franchise continued to show its strength among older viewers. CBS easily won total viewers for prime time with 14.4 million, ahead of NBC’s 9.2 million, ABC’s 8.4 million and Fox’s 5.5 million.

The main contributors to CBS’s big win in total viewers were “NCIS” with 17.8 million (3.0 average rating in 18-49) and “NCIS: Los Angeles” with 14.5 million (3.0 in 18-49).

At ABC, struggling “Private Practice” didn’t get much help from its lead-in, the “Dancing with the Stars” results show, which equaled last week’s season low with a 2.3 in adults 18-49. The network’s night opened with a bump for the season finale of “Last Man Standing” at 8 p.m., up two-tenths of a ratings point to a 1.7, while “Cougar Town” also rose two-tenths, to a 1.5.

Fox had an upbeat night, with “Glee” rising one-tenth to a 2.6 in 18-49 and the season finale of “New Girl” surging six-tenths to a 2.8.