The opening game of hockey’s Stanley Cup Final on NBC dominated Wednesday’s primetime ratings action in key demos, while CBS newcomer “The Briefcase” took a step back in its second outing after opening to good numbers a week ago.

According to preliminary national estimates from Nielsen, “The Briefcase” averaged a 0.9 rating/4 share in adults 18-49 and 5.4 million viewers overall in the 8 o’clock hour — down a sharp 36% (0.5) from its week-ago premiere. It tied in 18-49 with repeat ABC comedies “The Middle” (0.9/4 in 18-49, 4.5 million viewers overall) and “The Goldbergs” (0.9/3 in 18-49, 3.9 million viewers overall) and finished behind Fox’s “MasterChef” (1.45/6 in 18-49, 4.6 million viewers overall), which was down a bit from last week (1.6) but was once again the night’s No. 1 broadcast series in 18-49.

Despite the “MasterChef” decline, lead-out “Bullseye” (1.1/4 in 18-49, 3.3 million viewers overall) managed to hold at last week’s premiere rating, leapfrogging over “The Briefcase” as the top newcomer on the night in 18-49.

Elsewhere, ABC’s “Celebrity Wife Swap” (1.0/4 in 18-49, 3.5 million viewers overall) was down a tick in the demo and up a bit in total viewers from last week. It was preceded by repeats of 9 o’clock-hour comedies “Modern Family” (1.2/4 in 18-49, 4.4 million viewers overall) and “Black-ish” (1.1/4 in 18-49, 3.8 million viewers overall).

At NBC, Game 1 of the Stanley Cup Final between the Chicago Blackhawks and Tampa Bay Lightning averaged a 1.8 rating/6 share in adults 18-49 and 5.5 million viewers overall, with these numbers expected to stay at this level or perhaps slightly rise in the nationals. Last year’s opener between the Los Angeles Kings and New York Rangers did a 1.7 demo rating and rose to a 1.9 in the nationals.

In Chicago, the Blackhawks’ 2-1 victory delivered a whopping 18.4 rating/53 share in adults 18-49. And in Tampa, it pulled a strong 11.2/31.

CBS followed “The Briefcase” with encores of “Criminal Minds” (1.0/4 in 18-49, 6.1 million viewers overall) and “CSI: Cyber” (0.9/3 in 18-49, 5.9 million viewers overall). And CW aired repeats of “Arrow” (0.3/1 in 18-49, 1.0 million viewers overall) and “Supernatural” (0.2/1 in 18-49, 0.8 million viewers overall).

Preliminary 18-49 averages for the night: NBC, 1.8/6; Fox, 1.3/5; ABC, 1.0/4; CBS, 0.9/3; CW, 0.3/1.

In total viewers: CBS, 5.8 million; NBC, 5.5 million; Fox, 4.0 million; ABC, 3.9 million; CW, 0.9 million.