NBC’s “The Biggest Loser” was a hefty winner in its three-hour finale Tuesday, capturing its final two hours in demos with the net’s best perf on the night in 3½ years.

“Loser” has been an unsung standout for the fourth-place network. Though it is overshadowed on the night by TV’s top-rated show (Fox’s “American Idol”) and primetime’s hottest newcomer of the season (CBS’ “The Mentalist”), this season’s winter/spring couples edition ranks as “Loser’s” most-watched since its inaugural season in 2004-05.

And by airing two editions a season — and most weeks clocking in with two-hour installments — “Loser” has provided roughly 65 hours of solid programming for the Peacock.

In its finale on Tuesday, “Biggest Loser” averaged a plus-size 4.7 rating/13 share in adults 18-49 and 11.85 million viewers overall, according to Nielsen. This is the highest-rated episode of the show since “The Biggest Loser 3” wrap-up episode in December 2005.

“Loser” grew throughout the night, opening with a 3.2/10 in the demo opposite “Idol” and then building to a 5.6/15 at 10:30 p.m., when it beat the combined ABC-CBS delivery in the half-hour.

The couples edition of “Loser” finishes up more than 15% in both 18-49 and total viewers over fall’s families edition — despite the tougher competish in the winter and spring from “American Idol.”

And for the night, NBC’s 4.7 average in adults 18-49 reps its best on a Tuesday (excluding nights of the Olympics) since the December 2005 conclusion of “Biggest Loser 3.”

Elsewhere Tuesday, Fox won the night in all key measures behind the penultimate performance seg of “American Idol” (8.0/23 in 18-49, 22.71m from 8 to 9:05 p.m.) and the season finale of rookie drama “Fringe” (3.9/10, 9.28m from 9:05 to 10:01 p.m.).

CBS was solid with “NCIS” (3.3/9, 16.19m) and “The Mentalist” (3.3/8, 16.21m), while ABC’s lone decent hour was the 9 o’clock “Dancing With the Stars” results show (3.1/8, 14.06m).

CW saw “90210” log its best numbers since moving to 9 p.m. in March (1.2/3 in 18-49, 2.08m). Its 18-34 (1.7/5) number was just a tick behind ABC’s “Dancing” in the hour.

In cable, the NBA Playoff contests pitting the Boston Celtics against the Orlando Magic and the Los Angeles Lakers against the Houston Rockets both averaged around 5.2 million viewers on TNT.

At Bravo, the premiere of “Real Housewives of New Jersey” set records for an opening “Housewives” installment, garnering 1.72 million viewers (including 1.26 million adults 18-49). And the “Real Housewives of New York City” reunion spec pulled in 2.29 million viewers.