Oh no, you're on clay to boot? That slows the game down anyway, obviously.
At 3.5, I'd make sure you're moving him around, corner to corner, and like you said don't try to kill the ball. You just can't make unforced errors against these guys because they thrive off of that.
You also have to decide what your goal is in the match. If you want to work on your game and not care about the results then that is perfectly valid. But if you want to win, I think you figured out the strategy when you won 2 games in a row.
We may have already discussed it in this thread, can't remember, but have you read Winning Ugly?