"I Ain't Down Yet" as sung by Tammy Grimes and her brothers in THE UNSINKABLE MOLLY BROWN(1960). It was a rousing number and a great Act One opening. Unfortunately, Act Two was downhill all the way; you could say that it sank.
Also, I don't think that overtures should be considered as "opening numbers". Most overtures are great IMO, even overtures to flops.
Ragtime - Ragtime Overture/Statues and Stories (depending on which you consider the opening) - The Light in the Piazza In the Heights - In the Heights Willkomen - Cabaret I Hope I Get It - A Chorus Line Fancy Dress - The Drowsy Chaperone
http://www.beintheheights.com/katnicole1 (Please click and help me win!)
I chose, and my world was shaken- So what? The choice may have been mistaken,
The choosing was not...
"Every day has the potential to be the greatest day of your life." - Lin-Manuel Miranda
"And when Idina Menzel is singing, I'm always slightly worried that her teeth are going to jump out of her mouth and chase me." - Schmerg_the_Impaler
"Rent"--Rent "I Hope I Get It"--A Chorus Line "It's Your Wedding Day"--The Wedding Singer "Ragtime"--Ragtime "Another Openin', Another Show"--Kiss Me, Kate
among many, many others
A little swash, a bit of buckle - you'll love it more than bread.