It was the first Academy Award for both the actors and Leo, 50, drew laughter from the crowd when she uttered a cuss word during her acceptance speech.
Leo's gong was presented to her by 94-year-old screen legend Kirk Douglas, who made a joke out of the fact that he has never won the coveted golden statue himself.
Leo who won over Helena Bonham Carter (The King's Speech), Hailee Steinfeld (True Grit), Jacki Weaver (Animal King and Amy Adams (The Fighter), told the veteran,"You pinch me." "I know there's a lot of real lovely people who've said a lot of nice things to me for several months but I'm just shaking in my boots right now," she added.
And when Bale was handed his trophy by 'Legally Blonde' star Reese Witherspoon, he made a special mention of Leo's acceptance speech.
"Melissa you dropped the F-Bomb, I was planning to do that," he said before going onto thank, Dicky Eklund, who he played in the movie, asking the retired fighter to take a bow in the audience.
The 37-year-old then went on to thank his "beautiful wife" and his daughter "who has already taught me a lot more than I could ever give back to her."
Bale was competing with John Hawkes ("Winter's Bone"), Jeremy Renner ("The Town"), Mark Ruffalo ("The Kids Are All Right") and Geoffrey Rush ("The King's Speech") for the award.