The London Games produced its lowest-rated night to date Thursday, though NBC still beat the other broadcast networks combined. Ratings on the competition, meanwhile, appear to be artificially inflated by local preemptions for NFL exhibition games.

According to preliminary national estimates from Nielsen, the Summer Olympics on NBC averaged a 6.8 rating/20 share in adults 18-49 and 22.4 million viewers overall during primetime, with the show’s numbers expected to rise some in the nationals. The night, highlighted by track and field, women’s diving, beach volleyball and bicycle motocross, was the lowest rated of these Games and off a bit vs. the comparable night from Beijing four years ago. Events continue through Saturday night on NBC, with the Closing Ceremonies set for Sunday night.

At second-place CBS, encores of ”The Big Bang Theory” (1.8/6 in 18-49, 6.9 million viewers overall) and ”Two and a Half Men” (1.7/5 in 18-49, 6.2 million viewers overall) were followed by gains for ”Big Brother” at 9 (2.1/6 in 18-49, 6.2 million viewers overall). Closing out the night was a repeat of ”Person of Interest” (1.1/3 in 18-49, 4.7 million viewers overall). The Eye was preempted by football in Boston, Atlanta and Pittsburgh.

ABC saw ”Wipeout” perk up at 9 (1.7/5 in 18-49, 4.8 million viewers overall), and 10 p.m. drama ”Rookie Blue” was on the high side as well (1.5/4 in 18-49, 5.0 million viewers overall). In the opening hour, an encore ”Wipeout” did pretty well in the prelims too (1.6/5 in 18-49, 5.3 million viewers overall). Football preempted the net’s lineup in Philadelphia and Baltimore.

Also up, rather sharply, were Fox’s encores of ”Raising Hope” (1.1/4 in 18-49, 2.6 million viewers overall at 8 p.m. and 1.1/3 in 18-49, 2.8 million viewers overall at 8:30 p.m.) and ”Glee” (1.0/3 in 18-49, 2.7 million viewers overall). The net had just one preemption, but it was a big one (in Chicago).

Univision’s ”La Que No Podia Amar” hit another high in the 10 p.m. hour (1.9/5 in 18-49, 4.8 million viewers overall) leading up to its finale tonight.

Preliminary 18-49 averages for the night: NBC, 6.8/20; CBS, 1.7/5; ABC, 1.6/5; Univision, 1.5/4; Fox, 1.0/3; CW, 0.3/1.

In total viewers: NBC, 22.4 million; CBS, 5.8 million; ABC, 5.1 million; Univision, 4.0 million; Fox, 3.3 million; CW, 0.8 million.