This Is Us is still a hit, and it’s getting bigger. Season two of NBC’s family tearjerker opened Tuesday with the show scoring its best-ever same-day score in the Peacock’s target audience of adults under 50, with a preliminary 3.8 Nielsen rating. That’s up from last spring’s freshman finale (3.4) and way up from its series premiere last September (2.8 rating). Also encouraging for NBC: Us made these demo gains even though the show’s overall same-day audience (12.6 million) was pretty much flat versus the March finale. That means Us is adding the kinds of viewers (read: young) advertisers crave (and pay a premium to reach). Plus, these early numbers indicate Us has avoided the sophomore slumps now common for network shows, where declines of 10 to 20 percent between seasons are now almost expected. One note of caution, though. Fox’s Empire also followed up its hit season one in 2015 with an even bigger season-two premiere — and then began a fast fade in the ratings. As encouraging as today’s numbers are for NBC, This is Us — like every modern-day network series — will have to fight to hold on to its viewers.