Ways to improve defensive skills Last night I played two OTB games with a friend of mine and in both games I reached decent, even winning positions. At some moment though I overlooked my king safety and blundered horribly, which lead to losing both games.

Going back further it occurred to me that I do this almost on a regular basis! I reviewed few games in which I had a great position and then I made a bad move which lead to either the position being equal or even being worse. In these games the problem was not the king safety in particular, but some other positional or tactical error.

I've identified the problem as being too focused on attacking, trying to checkmate my opponent, then I relax a bit too much, thinking I'm winning, and make a bad move. Obviously, I need to work on avoiding blunders and improving my OTB analytical skills, but in this question I would like to focus on improving purely defensive skills, especially when under pressure.

One very important aspect of defense, as defined as Nimzowitsch, is the term of prophylaxis. The thing is that I'm not certain when I should make a prophylactic move that doesn't throw my advantage away as well.

One way for improvement in finding prophylactic moves would be studying the games of world class players, famous for their defensive skills and strong positional understanding. The name of Tigran Petrosian immediately comes to mind, but where would I be able to find some of his annotated games so I can really understand and appreciate the strength of his moves?

What other players would you recommend to study in order to improve in this particular area?

Maybe the most crucial question would be the following:

How to deal with the psychological pressure of having a great position and having it collapse over the next few moves?

What other ways for improvement would you recommend?
"...where would I be able to find some of his annotated games so I can really understand and appreciate the strength of his moves?"

Although you can find annotated games of Petrosian all over YouTube and some chess-related websites, I would recommend purchasing these books if you are interested in his style.

What other players would you recommend to study in order to improve in this particular area?

Karpov, Korchnoi, Ulf Andersson, Kramnik, Carlsen, Fischer.

How to deal with the psychological pressure of having a great position and having it collapse over the next few moves?

From personal experience, during the game just train yourself to not get too excited during the attack and before making the next attacking move spend time analysing how much of your defence get's hindered and how critical can that be in the long run. If the position is already collapsing, then either continue attacking if you are fully sure you will be able to checkmate faster than your opponent, or come back to defend and hope for a blunder or draw. After the game, analyse the game, just as you did.

What other ways for improvement would you recommend?

I would recommend playing as much games against higher rated opponents as possible. Thats the way I personally improve.