The most common and most likely answer to this crossword clue is the 7 letter word KETCHUP
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More clues leading to the result KETCHUP
Buddy explains!

The straight part
We know that "sauce" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sauce = ketchup.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KETCHUP mean?
KETCHUP noun- A tomato-vinegar-based sauce, sometimes containing spices, onion or garlic, and (especially in the US) sweeteners.
- Such a sauce more generally (not necessarily based on tomatoes).
- To cover with ketchup.