Mexican filmmaker Alfonso Cuaron won the Best Director honour for his black-and-white semi-autobiographical film "Roma".
It is the second Best Directing Award for Cuaron who had earlier won it for space drama "Gravity" in 2014.
"I thank the Academy for recognising a film centred on an indigenous woman, one of the 70 million domestic workers without workers' rights," Cuaron said at the gala on Sunday night.
He described "Roma" as a film that brings to the fore the sort of character more often relegated to the background in films, "at a time when we are being encouraged to look away".
Cuaron also thanked his actors Yalitza Aparicio and Marina de Tavira, saying "they are the film".
"Gracias, Gracias, Gracias," he ended his speech in Mexican style.
The Best Director award rounded off his total win at Oscars 2019 at three trophies -- first for the Best Cinematography and then for Best Foreign Language Film.
Cuaron received four nominations in four different award categories for the same film this time. He is only the fourth person with the feat.
He missed out on the Best Picture Award, which went to "Green Book".