Is it possible to discount 1 item when multiples are purchased?

in Development
Scenario: customer purchases 3 of the exact same item and hands over a coupon for x% off one item.
We found that the discount was applied to all 3 items and not just one (took some creative thinking to correctly charge the customer).
This is not an unusual practice so I have to assume we've set something up incorrectly. Any thoughts?
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