Nice starts for “The Marriage Ref” on Thursday and “Dateline” on Friday have helped NBC accomplish its goal of letting auds know it’s back in the 10 p.m. game.

A revamped lineup of new and returning series — promoted during the net’s 17-night coverage of the Winter Olympics — bowed last week, taking over for the short-lived “The Jay Leno Show” and performing nicely above average. Jay Leno’s second stint as host of “The Tonight Show” got off to an encouraging start, easily winning the week.

But the big question is, can the Peacock keep it up — in primetime with lead-ins that aren’t as strong, and in latenight without blockbuster guests?

NBC’s best 10 o’clock numbers last week came Thursday, where “The Marriage Ref” (3.4 rating/10 share in adults 18-49, 7.71 million viewers overall) won its hour among young adults over CBS’ “The Mentalist” (3.2/9 in 18-49, 14.87m) and ABC’s “Private Practice” (2.7/8, 7.57m), logging the net’s best non-Olympics score in the slot since the series finale of “ER” in April 2009. In its second half-hour, though, a declining “Ref” won by only a tick over the Eye crime drama (3.2/9 to 3.1/9), which won the hour rather comfortably in adults 25-54.

And “Marriage Ref” won’t enjoy nearly as strong a lead-in this week with “30 Rock” as it did preceding its premiere last Thursday with an hourlong seg of “The Office” (4.7/12 in 18-49, 9.02m). Workplace laffer, featuring the birth of Jim and Pam’s baby, won out in 18-49 for the first time over an original episode of ABC’s “Grey’s Anatomy” (4.0/11, 11.83m).

NBC also won’t enjoy as much support Monday (where “Law and Order” will follow “Trauma”) or Wednesday (where “Law and Order: SVU” will follow its own encores). Net effectively used two-hour episodes of both “Law and Order” series last week to give their returns a higher profile and to strengthen itself as much as possible from 10 to 11.

For the week, NBC averaged a 2.7 “live plus same-day” 18-49 rating during the 10 o’clock hour, well above the 1.6 it had averaged this season (mostly with “The Jay Leno Show”).

The stronger performance in the final hour of primetime also had to help NBC’s “Tonight Show With Jay Leno,” whose preliminary “live plus same day” 18-49 average for its first week back (1.5) easily bested CBS’ “Late Show With David Letterman” (1.0). The Peacock program also rolled in total viewers (5.6 million to 3.7 million), a reversal of the comfortable advantage “Late Show” had enjoyed this season opposite a Conan O’Brien-hosted “Tonight Show.”

Leno benefited from a strong lineup of guests last week, including Sarah Palin, Brett Favre, the cast of “Jersey Shore” and several gold medal-winning U.S. Olympians.

Of note on Friday, a two-hour “Dateline” (prelim 1.7/6, 7.2 million) was competitive from 9 to 10 p.m. and then pulled to the 18-49 lead from 10 to 11 p.m. (prelim 1.9/6), with CBS’ “Numbers” taking the hour narrowly in adults 25-54 and total viewers.

Unlike the week’s other two-hour special episodes, “Dateline” will continue to air from 9 to 11 on Fridays, giving the net a chance to regularly win or, at the very least compete for, the 10 p.m. lead.

Earlier Friday, the net had reason to be pleased with the premiere numbers for genealogical alternative series “Who Do You Think You Are” (prelim 1.6/6 in 18-49, 6.9 million viewers overall), which pulled to within a tick of CBS vet “Ghost Whisperer” (1.7/6, 7.4 million) for the demo lead at 8.