“Marvel’s Agent Carter” opened to decent but unexceptional ratings for ABC on Tuesday night, placing second to the strong “NCIS” shows on CBS and outperforming most of this season’s “Agents of SHIELD” numbers, but losing steam in its second half.

Nearly 16 months after Marvel’s “Agents of SHIELD” opened to blockbuster ratings (4.7 rating in 18-49, 12.1 million viewers overall), the limited series “Agent Carter” did a 1.9 rating/6 share in adults 18-49 and 6.7 million viewers overall — a rating that tops all but the premiere episode of “Agents of SHIELD” this season. Nobody expected the newcomer to match those “SHIELD” numbers, but a 1.9 for a heavily hyped premiere is rather middling.

“Agent Carter” lost some young-adult viewers as it progressed, starting with a 2.0 rating for the first two half-hours (strong for ABC in the time period) before slipping to a 1.9 at 9 p.m. and a 1.7 by 9:30. The rating for the final half-hour is the same delivered by the fall finale of “Agents of SHIELD.”

Based on a supporting character who appeared in the “Captain America” movies, “Agent Carter” will regularly air at 9 p.m., filling the “Agents of SHIELD” timeslot for the winter.

CBS won Tuesday behind “NCIS” (2.8/9 in 18-49, 19.5 million viewers overall) and “NCIS: New Orleans” (2.5/7 in 18-49, 17.4 million viewers overall) — the top two shows of the night in demos as well as total viewers. Both shows matched their season highs in 18-49, with “NCIS” drawing its largest overall audience in nearly a year.

In the night’s 10 p.m. hour, CBS’ “Person of Interest” (1.7/5 in 18-49, 10.0 million viewers overall) tied in 18-49 with NBC’s “Chicago Fire” (1.7/5 in 18-49, 6.7 million viewers overall), with the former falling off sharply from its lead-in while the latter spiked from its own. ABC’s “Forever” (1.1/3 in 18-49, 4.9 million viewers overall) remained a distant third and didn’t seem to get any bump from “Agent Carter.”

Fox finished close behind “Agent Carter” in the night’s opening hour with the premiere of the new “MasterChef Junior” season (1.8/5 in 18-49, 5.3 million viewers overall), matching the demo score of its fall-season premiere. The cooking competition ranked second among the Big Four for its hour in adults 18-34 (1.4/5).

Fox won the comedy battle in the 9 o’clock hour, with an above-average “New Girl” (1.5/4 in 18-49, 3.2 million viewers overall) easily besting NBC’s “Marry Me” (0.8/2 in 18-49, 2.0 million viewers overall). It was closer at 9:30 p.m., with Fox winning in 18-49 over NBC’s “About a Boy” (1.0/3 to 0.8/2) while the latter prevailed in total viewers (2.7 million to 2.2 million).

These are season lows for the NBC comedies, which have fallen off sharply from their earlier numbers when they were propped up by “The Voice.” “Parks and Recreation,” which has its final-season premiere next week, led into “Marry Me” last night with a repeat (0.8/2 in 18-49 and 2.1 million viewers overall).