Which of these primetime night soap operas was the first to premiere on U.S. TV?

From the four, "Dallas", released on April 2, 1978— May 3, 1991, first premiered as a primetime night soap opera on the CBS Television Network in the US.

"Dallas", the saga of the Ewing family and its massive oil empire, focuses on Jock Ewing as the patriarch and his three sons (Bobby James Ewing, the youngest; John Ross "J.R." Ewing Jr., the eldest and a covetous, egocentric, manipulative and amoral person; and Garrison Arthur "Gary" Ewing, the middle son who is seen as the family's weakest link). J.R. is an relentless CEO of Ewing Oil and is obviously more malicious than Bobby and Gary. Over a decade-plus of backstabbing, lust, greed, and inbreeding, dozens of characters enter and exit the "Dallas" universe.

The December 1979 to May 1993 "Knots Landing" is a US primetime night TV soap opera that also aired on CBS. It was a spin-off of "Dallas", and it was set in a fictitious coastal suburb of Los Angeles, California. It initially centered on the lives of four married couples living on a cul-de-sac, Seaview Circle.

"Dynasty" is a US primetime night TV soap opera that aired on ABC from January 12, 1981—May 11, 1989. This series revolves around the Carringtons, a wealthy family residing in Denver, Colorado.

"Falcon Crest", another US primetime night TV soap opera, aired for 9 seasons on CBS. It ran from December 4, 1981 until May 17, 1990. This is a series which looks at the feuding factions of the wealthy Gioberti/Channing family in the California wine industry.