NBC ruled the Tuesday night ratings race in key demos behind an expanded installment of “The Voice” and a dominant performance by “Chicago Fire,” with the drama kicking off a three-show crossover storyline.

Elsewhere, a slew of shows on the competition hit lows, including ABC’s “Marvel’s Agents of SHIELD” and CBS’ “Person of Interest,” but Fox’s “MasterChef Junior” had a strong second-week showing leading off the night and CW’s “The Flash” continued to shine.

According to preliminary national estimates from Nielsen, NBC swept Tuesday’s half-hours in adults 18-49 starting with the second night of the live playoffs on “The Voice” (2.9 rating/9 share in adults 18-49, 11.2 million viewers overall). The music contest was on par with its prior Tuesday original of two weeks ago and was Tuesday’s No. 1 show in 18-49, 25-54 (3.9/10) and all female demos.

“Chicago Fire,” which had been losing some steam as expected with comedies as its lead-in, shot back up last night (2.2/7 in 18-49, 9.1 million viewers overall), drawing nearly as many young adults as the CBS and ABC dramas in its time period combined. The drama, which was starting a storyline that concludes tonight with “Law & Order: SVU” and “Chicago PD,” rose 29% from its last original (1.7) for its best score since its second episode of the season (Sept. 30).

At CBS, which dominated the night as usual in total viewers, “NCIS” (2.3/7 in 18-49, 17.4 million viewers overall), “NCIS: New Orleans” (2.0/6 in 18-49, 14.9 million viewers overall) and “Person of Interest” were all down 0.2 or more from their most recent originals to set lows in 18-49. “NCIS” was the night’s No. 1 scripted series in 18-49 and 25-54 (3.6/10) while also easily standing as the most-watched program overall.

At Fox, “MasterChef Junior” (1.8/6 in 18-49, 4.8 million viewers overall) impressively matched its season premiere of last week when it went up against considerably softer competition, and outperformed last year’s comedies in the hour on the comparable night (“Dads” and “Brooklyn Nine Nine”) by 38% (1.8 vs. 1.3). Comedies “New Girl” (1.3/4 in 18-49, 2.9 million viewers overall) and “The Mindy Project” (1.0/3 in 18-49, 2.5 million viewers overall) were both down from their season highs of last week and each also came in 0.4 lower than the comparable night a year ago.

ABC had another sluggish start to Tuesday, with “Selfie” (0.9/3 in 18-49, 3.3 million viewers overall) matching its low of last week and ranking fifth among the English-language broadcast networks in the 8 o’clock half-hour. A special “Modern Family” repeat couldn’t do any better at 8:30 p.m. (0.9/3 in 18-49, 2.9 million viewers overall), and “Marvel’s Agents of SHIELD” (1.5/4 in 18-49, 4.3 million viewers overall) was down a tick from its prior original to set a series low. Also down a tenth to its low was rookie 10 p.m. drama “Forever” (1.0/3 in 18-49, 4.2 million viewers overall).

Like the CBS dramas from 9 to 11 p.m., ABC’s dramas likely were affected by the stronger-than-usual performance by NBC with its extra hour of “The Voice” and “Chicago Fire’s” stunt storyline.

CW’s “The Flash” (1.4/4 in 18-49, 3.4 million viewers overall) didn’t miss a beat as it returned following its first repeat; it was up or steady vs. its prior original in just about every category and outperformed last year’s “The Originals” by 21% in 18-49 (1.4 vs. 1.1). It was followed by the 200th episode of “Supernatural” (0.9/3 in 18-49, 2.2 million viewers overall) was up a bit from its prior original (though down from last year).

Preliminary 18-49 averages for the night: NBC, 2.7/8; CBS, 1.9/6; Fox, 1.5/4; ABC and Univision, 1.1/3; CW, 1.1/3; Telemundo, 0.5/2.

In total viewers: CBS, 13.8 million; NBC, 10.5 million; ABC, 3.9 million; Fox, 3.8 million; Univision, 2.9 million; CW, 2.8 million; Telemundo, 1.3 million.