[pm215]

I'm British, and I refer to ketchup as ketchup. This may be regional; I'm southern-English. I'd probably by default assume that if you said 'tomato sauce' you meant a generic tomato-based sauce, not the specific condiment Heinz &c make.

[jfk13]

Also southern English, and this matches my understanding of the terminology. But yes, I believe usage does vary regionally.