How do you make a BBQ sauce less sweet? Add lemon?

I would also try adding some spice to offset the sweet. Chili powder or fresh chilies, onion, or shallots add a nice compliment to sweet flavor profile.

I agree with the vinegar addition. Cut back on the sweet ingredient, probably brown sugar, and add more vinegar.

Vinegar, the apple cider variety would be a good choice.

Tamarind paste.

Depends on other ingredients. More tomato sauce? More mustard? Ive sometimes solved that problem with a bit of soy sauce