Not sure if this qualifies -- it's both more than 10 years old, and not really a computational complexity result in itself -- but I think the pair of {Graph Structure Theorem, Graph Minor Theorem} is worth noting. It was completed in 2004, and establishes an equivalence between "Bounded topological complexity" and "Does not contain some finite set of minors". Each theorem establishes one direction of the equivalence.
This has primarily had an impact within the realm of parameterized complexity theory, where one of these measures is often bounded, allowing for efficient algorithms that leverage the other. So, I would say that these results have had substantial impact on computational complexity, even if they do not come directly from that field themselves.