WEST HOLLYWOOD, Calif. — The champagne was flowing. HBO had just capped off another triumphant night at the Emmys, and it was time to party in the courtyard of the mammoth Pacific Design Center.

At every turn, there was another show celebrating on Sunday night. The cast of “Game of Thrones” convened for one last time to toast another win for best drama, its Emmy record-tying fourth victory in the category. John Oliver’s “Last Week Tonight” overwhelmed his late-night competition to win best talk show for a fourth straight year. “Chernobyl,” HBO’s unexpected gem of a limited series about the 1986 nuclear reactor disaster, took home best limited series. And the network topped Netflix for most Emmy wins over all, reclaiming sole bragging rights after tying with the streaming service last year.

“Unparalleled,” said John Stankey, the chief executive of Warner Media, HBO’s parent, as he stood right in the middle of the party. “Absolutely unbelievable.”

[Read about the best and worst moments at the Emmys. See the full list of winners.]

Now comes the hard part. HBO, after years of dominance, is at a crossroads.