Having suffered achilles tendonitis as well as plantar fasciitis I'll echo those that mentioned insoles. For me, Superfeet green help keep me pain free. I've been wearing Nike Vapor X with the Superfeet for several months with zero pain. I'm very particular about the fit of my shoes so I always try on potential new shoes with my Superfeet and the 2 pair of socks I wear when I play. Shoes may fit and feel different with the insoles replaced.
I have insoles in all my tennis shoes. I suffered PF last year, and can still feel the remnants of it. The insoles I use are specifically for low arch support with a bump under the middle of the foot. In addition, I use Birkenstocks (Arizona). Yes, they're not the best fashion statement, but my feet love them. There's hardly any cushioning in Birks compared to a running shoe, but the shape of the sole makes all the difference. It's easily compared, if you walk around barefoot on a hard floor or wooden floor, and then put them on.
I can run without insoles without any issues, provided the shoes are ment for overpronation, like the Nike Structures. But playing tennis, I need the insoles, prob due to the fact that sometimes there's a lot of force abruptly applied to the footbed.