No, your prior post was correct.
I could play tennis well (past). It's possible you still play tennis well because you are referring to a time in the past and it makes no comment about how well you play today. When I was only 10, I could play tennis as well as my coach. But then I broke my wrist and I've never been able to get my game back. OR And I'm still quite good today, although now that I'm 80, I've slowed down a bit.
I can play tennis well (present).