Joaquin Phoenix accepts the award for best performance by an actor in a leading role for "Joker." AP

Joaquin Phoenix capped his awards season sweep with his first Oscar on Sunday for "Joker," besting a packed field of nominees that included Antonio Banderas, Leonardo DiCaprio, Adam Driver and Jonathan Pryce.

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His first Academy Award follows months of controversy over the arthouse origin story about Batman's nemesis, which stoked fears of inciting violence even as it hoarded nominations and awards.

Joaquin Phoenix, left, accepts the award for Best Actor for "Joker" from British actress Olivia Colman. AFP

"We share the same love, the love of film. This form of expression has given me the most extraordinary life," the actor said before launching into an emotional call for Hollywood to "use our voice for the voiceless" and "fight against injustice."

He ended his speech with a tearful tribute to his brother River, who died of an overdose in 1993 at age 23.

"Run to the rescue with love and peace will follow," Phoenix said, quoting his brother.