BrodyFosse123 said: "bwayphreak234 said: "Marge in Promises, Promises - Katie Finneran walked away with that revival."
And she only appears in Act 2! 
Not only that. The original Marge, Marian Mercer, won the first Tony for that role. Saw both and Finneran could not compare to Mercer.
Alice Playten stole Henry, Sweet Henry 50 years ago, but she lost her Tony nomination to Lillian Heyman, who stole Hallelujah, Baby, with a great show-stopping number. Leslie Uggams was great, but Heyman got the biggest applause at the curtain call.
I don't know if then unknown Joel Grey should count. Four people took their curtain call after him in the original production of Cabaret and their applause were tepid after his. I remember feeling sorry for Lotte Lenya having to come out right after him, because the applause were well down and no bravos. In those days, you would occasionally hear bravos, and Joel got a basketful.
One could argue that Bonnie Franklin in Applause fits the bill. Her two numbers both got the most applause the entire evening, and she received more applause at the curtain call than anyone but Lauren Bacall.
I don't know if Richard Henry Lee stole the show, but he had one hell of a rousing number that did stop the show.
To me, Daveed Diggs was the star of Hamilton; with a cast and roles like that one had, I am not sure he stole the show, great as he was.
Another example that I will put out and am not sure is really valid. Angela Lansbury in a large supporting role stole the show out from all the other members of the Blithe Spirit cast. I have never seen a show in which the audience applauded every single time that she came on stage, but they did for this one. Clearly, they were seeing a theatre legend who they loved; but the show was markedly more entertaining every time she was on stage.
A Thousand years ago, Maureen Stapleton, in a tiny role in a show that ran less than a week, stole the show uttering a single line, 'Norman, is that You'. The show was lousy, but it was heaven for the 5 minutes or so she was on stage.