This marks the second occasion on which he has beaten the statistical odds: It's only the fifth time in the past 25 years that Oscar has rewarded a previous victor; voters generally prefer to give the gold to first-timers.
Sunday's best picture Oscar - presented at the end of the 3-1/2-hour show - is seen as a close race between "The Shape of Water,"Three Billboards" and Universal Pictures racial satire "Get Out". It happens. And I want to tell you, everyone that is dreaming of using fantasy to tell the stories about the things that are real in the world today, you can do it".
Melvin said after decades of growth, Toronto's TV and film industries are truly "world-class".
"I have 35 years in the business now and worked in Toronto nearly exclusively, so I've worked with and watched the business grow in Toronto and go from children's television to Academy Award-winning films", he said.
As they accepted their trophies onstage, the trio thanked their colleagues back home in Toronto. "It's so nice seeing you again", said Beatty with a grin.
"Thank you to the academy".
The 90th Academy Awards, popularly known as the Oscars, are being held at the Dolby Theatre on March 5.
Del Toro, 53, is known for making both mainstream action movies like "Hellboy" and offbeat dark fantasies like "Pan's Labyrinth."The Shape of Water" has been celebrated as a visual feast about a woman who falls in love with a unusual amphibious creature".
Four out of the five winners for Best Director come from Mexico.
There was also the first nod in history for a female cinematographer, Rachel Morrison, who shot Dee Rees's racial drama "Mudbound" although the award ended up going to Roger Deakins on his 14th attempt, for "Blade Runner 2049".
Kimmel made a couple of jokes about the 88-year-old Toronto native's age, including a reference to the hit Broadway play "Hamilton", about one of the founding fathers of the United States.
A host of stars - including Jane Fonda, Lin-Manuel Miranda, Patrick Stewart and Richard Jenkins - sported Time's Up badges, civil rights ribbons as well as orange USA flags backing gun control. Kimmel teased Plummer from the stage.