NBC’s star-studded 75th-anni spec dominated the primetime ratings Sunday, giving the net its best May sweeps showing on the night in three years.

According to Nielsen prelims, the Peacock’s three-hour backslap averaged 20.4 million viewers and a 7.7/19 in adults 18-49. After being edged out by Fox’s “The Simpsons” in the demo at 8 (prelim 5.6/17 vs. 5.4/16), spec grew nicely and won easily the rest of the way by all key measures.

“NBC’s 75th,” which featured the likes of Jerry Seinfeld and Barbara Walters and reunited the casts of classic series such as “Hill Street Blues,” “Family Ties” and “Cheers,” peaked in the 9:30 half-hour in overall audience (23.5m) and the 10 o’clock half-hour in 18-49 (prelim 8.8/21).

Net also took Sunday’s opening hour in adults 18-49 with an NBA playoff overrun (projected 4.2/14) and was expected to win the night by 7 or 8 shares over Fox in the demo and by more than 5 million viewers over CBS in overall audience.

Other than the Olympics and Golden Globes, this is NBC’s strongest showing on a Sunday this season. It’s also the net’s best 18-49 delivery on a May sweep Sunday since the premiere of “Noah’s Ark” on May 2, 1999.

It was NBC’s fifth consecutive nightly victory in adults 18-49 and the sixth in seven nights. And if it wasn’t already a foregone conclusion, the Peacock now appears a lock to win the May sweep in adults 18-49 for an eighth straight season (including one tie) — having taken a roughly 35% advantage over CBS through Sunday (roughly 5.5 to 4.1).

Fox was least affected by NBC’s success, but was still down 20% week-to-week in 18-49. Key to the week-to-week decline was a slower start at 7 with “King of the Hill” (prelim 2.1/8), down 36% from last week’s “Simpsons” repeat (3.3/11).

ABC and CBS both had sluggish nights. The Alphabet’s savior was “The Practice” at 10 (prelim 14.1m, 4.8/17 in 18-49), while the Eye’s “Hallmark Hall of Fame” pic “Little John” fared decently given the tough NBC competish (prelim 13.4 million, 2.9/7).

NBC also did pretty well with sports over the weekend.

On Saturday, its second year of televising horse racing’s “Kentucky Derby” (5:30-6:45 p.m. EDT) generated a 9.3 rating/21 share in overnights, down a tick from last year. The pre-race coverage from 5-5:30 EDT did a 6.1/15, up 9% year-to-year.

And on Sunday, the competitive Lakers-San Antonio Spurs contest became the net’s highest-rated playoff game of the season (7.4/15 in overnights). That game was alone among the net’s four weekend playoff games to improve upon last year’s ratings, though.