“Tonight Show with Conan O’Brien” scored a 7.1/17, according to Nielsen Media Research, the highest overnight ratings performance for a Monday-night installment of the latenight program in four years. Show also scored the highest numbers for the night for any show -- primetime or latenight.

 

However, O’Brien’s debut as host of NBC’s 55-year-old latenight institution failed to match Friday’s “Tonight Show” finale for Jay Leno, which drew an 8.8/20 in the same Nielsen metered markets.

 

Of course, regardless of whether O’Brien is ultimately able to match the popularity of his predecessor -- who took over the seat from Johnny Carson in 1992 and is ready to assume control of a new NBC show at 10 p.m. in the fall -- 11:30 will be a lot bigger for him than 12:30.

 

In fact, O’Brien’s debut at the earlier slot, which included actor Will Ferrell as a guest and Pearl Jam as the music performer, was up 173% over his “Late Night with Conan O’Brien” finale in February. O’Brien’s last turn at the 12:30 slot generated his biggest audience since January 2005, netting a 2.6/8.

 

With O’Brien behind the “Tonight Show” desk Monday, the program stayed dominant in the time period, routing CBS’ “Late Show with David Letterman” (2.8/7) and ABC’s “Nightline” 2.7/6.

 

Even better for NBC, “Late Night with Jimmy Fallon” – the successor to O’Brien at 12:30 – had its best Monday night ratings ever, a 2.5/9, even besting the show’s March 2 premiere.

 

While capturing a primetime-like 7.1 rating isn’t shabby for a premiere, the numbers won’t stay that huge. O’Brien’s ratings performance is expected to even out into a more latenight-like profile over the next few weeks.