Several strong series premieres and a monster return by Fox’s “Empire” highlighted the opening week of a 2015-16 television season in which the networks did their best to defy ratings gravity.

On the heels of a summer that saw the vast majority of established broadcast and cable series take a tumble in the ratings, it was not surprising that the Big Four networks came back softer as well. With the exception of a handful of shows like ABC’s “The Middle” and “The Goldbergs” and CBS’ “The Amazing Race” and “Blue Bloods,” every other returning series on ABC, CBS, NBC and Fox were down from their year-ago premieres in same-day ratings estimates from Nielsen.

As a result, the Big Four were down about 10% in all key categories, including adults 18-49 (8.5 rating vs. 9.5) and total viewers (31 million vs. 34.3 million).

It’s not only that there’s more product available on more screens than ever before, but fewer people in general are watching primetime television on a nightly basis. Nielsen estimates that tune-in was down across the board during Premiere Week, with the biggest declines coming among younger viewers.

For example, while roughly 54% of adults 55 and older were watching primetime during the first four nights of the season (a mere 1% decline from last year), the percentage of adults 18-49 watching (30.2%) was down from 7.6% from last year (32.7%). And among the younger 12-34 crowd, only 23.2% were watching on average Monday through Thursday, down 11.5% from a year ago (26.2%).

The Big Four spin-meisters continue to tout delayed and multi-platform viewing of their shows, as DVR playback, video-on-demand and streaming account for an increasingly large piece of the overall viewership pie. And this may help shows that opened low — including Fox’s “Minority Report” and NBC’s “The Player” — hang around longer than might be expected.

Most nights for the networks were down vs. last year in same-night viewership, but there were instances of the ratings picture brightening in “live plus-3.” ABC’s Wednesday, for example, was down 13% vs. last year in same-night numbers (thanks in part to tough competition from “Empire”) but that deficit was trimmed to 8% in year-over-year L3 comparisons. And CBS’ Tuesday drama lineup narrowed its decline from 16% to 11%. Small victories maybe, but it’s another sign that next-day numbers only tell part of the ratings story.

From a network standpoint, NBC took Premiere Week in adults 18-49 for a fourth straight year and extended its overall winning streak to 12 weeks — the longest stretch for any network since Fox’s “American Idol” heyday in 2009. The Peacock also won in adults 25-54 and adults 18-34 while CBS led comfortably in total viewers. The Eye has now won Premiere Week in total viewers for seven straight seasons.

It will take a few weeks to see where the networks settle in, as sports and other vagaries of the schedule make it hard to make too much of year-over-year comparisons during Premiere Week. CBS was the only network up vs. last year but that was thanks largely to an NFL overrun on Sunday. Fox, conversely, may have had monster year-over-year improvement on Tuesday and Wednesday, but it finished down from last year, when it had the NFL overrun leading into its big “Simpsons”-“Family Guy” crossover. And ABC’s Saturday college football game was down about 35% from last year.

All four networks had something to be pleased about in same-night premiere numbers for new shows. ABC’s “The Muppets” and “Quantico” looked good out of the gate, while CBS’ “Limitless” showed some spark on Tuesday and half-hour “Life in Pieces” opened OK. NBC’s “Blindspot” was a breakout hit while the net’s “Heroes” reboot “Heroes Reborn” was solid on Thursday.

Fox’s “Rosewood” surprised by winning its hour on Wednesday — with pre-“Empire” tune-in playing a big part in that. Another of the net’s new shows, Tuesday night’s “Scream Queens,” had a lackluster bow but jumped in delayed viewing and seems to be a good example of how much of a show’s audience can come after its linear premiere.

Looking at some same-day program highlights for the week, NBC’s “Blindspot” (3.1/10 in 18-49, 10.61 million viewers overall) became the net’s highest-rated drama premiere since “The Blacklist” in the same Monday-at-10 hour two years ago. It beat its combined ABC-CBS competition by 29% in 18-49 (3.1 vs. 2.4).

“The Voice” remained potent for NBC, averaging a 3.5 demo rating for its two-hour installments on both Monday and Tuesday and helping boost newcomer “Best Time Ever With Neil Patrick Harris” (2.1/7 in 18-49, 5.91 million viewers overall). “Best Time Ever” was up 14% (0.3) in 18-49 from its premiere and won its hour in the demo.

Wednesday’s “Mysteries of Laura” (1.2/4, 7.11 million viewers overall) outdelivered ten of its final 11 episodes from its rookie season, and lead-out “Law & Order: SVU” matched its top 18-49 rating (1.8) and drew its largest overall audience (8.27 million) for any non-crossover episode since last season’s premiere. And on Thursday, “Heroes Reborn” (2.0/6, 6.09 million) matched the network’s highest-rated drama premiere on the night since “Southland” in 2009.

At CBS, “Limitless” (1.9/6 in 18-49, 9.86 million viewers overall) had a good premiere, building by 0.2 on its lead-in from “NCIS: New Orleans” (1.7/6 in 18-49, 12.62 million viewers overall), which had a soft second-season premiere. The night’s standout for the net remains “NCIS” (2.5/9 in 18-49, 18.19 million viewers overall), which grew to 21.5 million total viewers in L3.

Monday comedy “Life in Pieces” (2.6/8 in 18-49, 11.28 million viewers overall) is the season’s top-rated new half-hour in adults 25-54 (3.8/10) as well as total viewers, though it’s losing big chunks of its “Big Bang Theory” lead-in.

ABC had eight of the week’s top 20 entertainment series on the Big Four in 18-49, led by “Scandal” (3.3/10 in 18-49, 10.25 million viewers overall), “Modern Family” (3.2/10 in 18-49, 9.46 million viewers overall) and “The Muppets” (2.9/11 in 18-49, 9.01 million viewers overall), which was the week’s No. 2-rated new series in the demo. Joining “Scandal” on the net’s strong Thursday were “Grey’s Anatomy” (2.8/10 in 18-49, 9.55 million viewers overall) and “How to Get Awy With Murder” (2.6/9 in 18-49, 8.38 million viewers overall), both of which were in the week’s top 15 programs.

On Sunday, “Once Upon a Time” (1.8/5 in 18-49, 5.93 million viewers overall) returned well behind its hot start of last season, but the net’s “Quantico” impressed closing out the night (1.9/6 in 18-49, 7.14 million viewers overall). The latter, the fall’s most critically acclaimed new broadcast drama, built by about 35% on its lead-in from another new series, “Blood & Oil” (1.4/4 in 18-49, 6.36 million viewers overall).

Fox’s big gun, of course, was “Empire” (6.7/21 in 18-49, 16.18 million viewers overall), which was making its fall debut after a 12-episode first season last spring. It was Premiere Week’s top entertainment program in 18-49, 25-54 (6.9/18) and 12-34 (5.9/24), rising about 75% above with its January premiere of last season. And it certainly helped lead-in “Rosewood” (2.4/9 in 18-49, 7.54 million viewers overall), which was the night’s No. 2 drama. Not so hot was Monday newcomer “Minority Report” (1.1/3 in 18-49, 3.10 million viewers overall).

CW sat out Premiere Week as usual, and will bring back its series starting next week, kicking off Oct. 6 with “The Flash.”

TOP PRIMETIME NETWORKS

(Sept. 21-27, 2015; live plus same-day)

Adults 18-49

NBC ……………. 2.7/9

CBS …………….. 2.5/8

ABC …………….. 1.7/6

Fox ……………… 1.6/5

UNI ……………… 0.8/3

USA …………….. 0.6/2

ESPN …………… 0.6/2

TBS ……………… 0.5/2

DISC ……………. 0.5/2

FX ……………….. 0.5/2

Total Viewers (in millions)

CBS ……………… 10.94

NBC ……………… 8.94

ABC ……………… 6.93

Fox ………………. 4.21

UNI ………………. 2.26

FNC ……………… 1.99

USA ……………… 1.81

TNT ……………… 1.80

DISC …………….. 1.79

ESPN ……………. 1.72

TOP PRIMETIME PROGRAMS

(Sept. 21-27, 2015; live plus same-day)

Adults 18-49 (rating/share)

1. Sunday Night Football: Denver-Detroit (NBC), 8.1/25

2. Empire (Fox), 6.7/21

3. Thursday Night Football: Washington-NY Giants (CBS/NFLN), 6.0/20

4. The Big Bang Theory (CBS), 4.7/17

4. Monday Night Football: NY Jets-Indianapolis (ESPN), 4.7/16

6. The Voice-Tuesday (NBC), 3.5/12

7. Fear the Walking Dead (AMC), 3.4/10

8. The Voice-Monday (NBC), 3.5/11

9. Scandal (ABC), 3.3/10

10. Modern Family (ABC), 3.2/10

11. Blindspot (NBC), 3.1/10

12. The Muppets (ABC), 2.9/11

12. 60 Minutes (CBS), 2.9/9

14. Grey’s Anatomy (ABC), 2.8/10

15. How to Get Away With Murder (ABC), 2.6/9

15. Life in Pieces (CBS), 2.6/8

17. NCIS (CBS), 2.5/9

17. Survivor (CBS), 2.5/9

19. Rosewood (Fox), 2.4/9

19. The Goldbergs (ABC), 2.4/8

19. Black-ish (ABC), 2.4/7

Total Viewers (in millions)

1. Sunday Night Football: Denver-Detroit (NBC), 22.07

2. The Big Bang Theory (CBS), 18.20

3. NCIS (CBS), 18.19

4. Thursday Night Football: Washington-NY Giants (CBS/NFLN), 16.88

5. Empire (Fox), 16.18

6. 60 Minutes (CBS), 15.04

7. NCIS: New Orleans (CBS), 12.62

8. Monday Night Football: NY Jets-Indianapolis (ESPN), 12.48

9. The Voice-Monday (NBC), 12.37

10. The Voice-Tuesday (NBC), 12.35

11. CSI (CBS), 12.22

12. Dancing With the Stars (ABC), 11.46

13. Life in Pieces (CBS), 11.28

14. Scorpion (CBS), 11.09

15. Blindspot (NBC), 10.61

16. Scandal (ABC), 10.25

17. Blue Bloods (CBS), 10.08

18. Limitless (CBS), 9.86

19. Survivor (CBS), 9.70

20. Dancing With the Stars (ABC), 9.58