Bright, enthusiastic and full of heart, Kara doesn't need her superpowers to be a hero … though they certainly don't hurt.

Forced to live in secret all her life while her famous cousin saves the day in Metropolis, Kara ( Melissa Benoist ) will finally become the hero she's always been destined to be when she's called upon in CBS' Supergirl series premiere.

The series opens up after 'Big Bang Theory' to a strong 3.1 rating in the key demo.

One of the fall's most anticipated premieres was also one of its last. CBS' Supergirl finally made its entry to the schedule on Monday night, and network brass likely think it was worth the wait.

In a onetime-only time slot of 8:30 p.m., the one-hour premiere averaged a strong 3.1 rating among adults 18-49 and 12.9 million viewers, per Nielsen Media's live-plus-same-day metrics. That makes Supergirl the fall season's most-watched new series debut for a first-night showing and ties it (with NBC's Blindspot) as the highest-rated.

Like all series, Supergirl stands to grow considerably with delayed viewing. ABC's Quantico, for example, more than doubled its Sunday showing with its latest live-plus-7 ratings. And veteran juggernauts like The Big Bang Theory continue to add upwards of two full ratings points with delayed viewing.

Speaking of The Big Bang Theory, Supergirl had the night's best possible lead-in from the comedy. Airing its last Monday original before shuffling back to Thursday nights when the NFL's eight-game pact with CBS wraps for the season, it averaged a 4.2 rating among adults 18-49 and 15.9 million viewers. Scorpion got no big lift from all the extra attention at the top of the night, averaging a steady 1.9 rating in the key demo.

Supergirl now shares bragging rights for the highest-rated same-day debut of the 2015-16 TV season with another Greg Berlanti-produced series, Blindspot. That bowed to a 3.1 rating in the key demo on Sept. 21. (As for Blindspot, it was the night's No. 3 scripted entry on broadcast, netting a 2.2 rating with 18- to 49-year-olds.)

NBC won the night with its pairing of Blindspot and The Voice — the latter steady with a 3.1 rating in the key demo, though there were NFL preemptions. ABC also had NFL preemptions, but Dancing With the Stars is thus-far steady with a 1.9 rating among adults 18-49.

Fox's Gotham managed to improve its same-day showing, despite the increased genre competition from Supergirl, up two-tenths of a point to a 1.5 rating among adults 18-49. Minority Report held the previous week's 0.6 demo rating.

Crazy Ex Girlfriend and Jane the Virgin were both reasonably steady on The CW, but both were off a tenth of a point for series lows — averaging a respective 0.2 and 0.3 rating among adults 18-49.

