CBS aired mostly repeats last night, but capped off prime time with its hit summer drama series — and the combination was just enough to win the night, based on Nielsen overnights for the key 18-49 demo.

TVbytheNumbers.com reports that "Under the Dome" was easily the top show of the night, airing at 10 p.m. and almost tripling its time-period competition with a 2.7 average in 18-49 — equaling last week’s number.

Trailing "Dome" at 10 p.m. were originals from two rival broadcast nets — ABC’s "Mistresses," with a 1.1 in the 18-49 demo (slipping one-tenth from a week ago), and NBC’s "Siberia," which delivered a 0.8 (also losing one-tenth).

The comparisons were just as striking in total viewers: 10.8 million for "Under the Dome," 3.6 million for "Mistresses" and 2.5 million for "Siberia."

Earlier in the night the big number was a 1.9 average rating in adults 18-49 for ABC’s two-hour "The Bachelorette," which matched last week’s average. The combination helped ABC finish a close second behind CBS for prime time overall.

NBC gave it a go with two hours of its own reality programming, but "American Ninja Warrior" lost one-tenth from a week ago to settle for a 1.5 in the 18-49 demo, and "Get Out Alive With Bear Grylls" also lost one-tenth, slipping to a 1.4.

Fox aired all repeats and wound up in fifth place.

An interesting development — but not in a good way — at the "sixth broadcast network," the CW, was the debut of the two-hour "iHeartRadio Ultimate Pool Party," which delivered one of the lowest demo numbers in recent memory, a 0.2 in viewers 18-49, along with 732,000 viewers.

The tally for prime time overall shows how narrow CBS’s win was, with Univision also knocking on the door. CBS came out on top in the 18-49 demo with a 1.7 average, followed by ABC (1.6 average), Univision (1.6), NBC (1.2), Fox (0.6) and CW (0.2). CBS had a little more breathing room in total viewers, winning the night with 6.7 million, followed by ABC (5.7 million), Univision (4.0 million), NBC (3.8 million), Fox (1.5 million) and CW (732,000).