Green’s Dictionary of Slang

(Aus./N.Z.) a horse; thus tomato sauces, the horses, i.e. horseraces.

1905		Duke Tritton’s Letter n.p.: A Pot And Pan driving a nice high stepping Tomato Sauce in a flash Big An’ Bulky pulled up and asked if I was looking for Dodge An’ Shirk.
1968		J. Alard He who Shoots Last 206: Wot tomato sauce is your mate Nippy ridin’ in da Cup?
2002		Pete’s Aussie Sl. Home Page 🌐 tomato sauce: a horse [...] tomato sauces: the horses, horse races.
2003		McGill Reed Dict. of N.Z. Sl.