The ONLY way to beat players that you get tense while playing, is to play those types of players more often. After a while you will see them as just another tough game, and you will do your thing. If you shy away from the problem it will only grow.
Recently I started playing in the top dog division of pool league. At first I was very intimidated, and struggled. Now that I've been playing it for a couple months, I just view them like anyone else. I still get nervous because of the pressure I put on myself to do well, but I'm not dogging balls because I'm playing a certain person.
I'd also add that win you get to a certain point where you just don't give a rip who you're playing, you can beat ANYONE. And I do mean ANYONE. If you don't give a shit that you're playing SVB, and you can break and run, it's real tough for him to beat you from the chair.
There are a few things that get said here A LOT, so much so, that they lose their true value. Here they are again.
YOU PLAY THE TABLE, NOT THE OPPONENT.
PLAY ***YOUR*** GAME, NOT THEIRS.
KISS ---> KEEP IT SIMPLE, STUPID.
You know how to make the shots, and get shape. Just do it.
All the best,