Haney, the former undisputed lightweight world champion stepping up to the 140-pound division for the first time, won by scores of 120-107 from all three judges and said the move up in weight had made a new fighter of him.
"A tremendous difference," a victorious Haney told DAZN in the ring at the Chase Center, home of the NBA's Golden State Warriors.
"You see it in my performance. I felt so much stronger... 140 got a new king."
Haney sent Prograis to the canvas in the third round with one of many devastating combinations.
He wobbled Prograis again in the sixth on the way to the dominant victory.
Haney, a Bay Area native, improved to 31-0 with 15 knockouts.
Hard-hitting southpaw Prograis was making the second defence of the WBC title he won with an 11th-round knockout of Jose Zepeda for the vacant title in November last year.
He notched a split-decision win over Danielito Zorrilla in June but fell to 29-2 with 24 knockouts with the defeat.
