zydeco: Petrosian has some interesting notes on this game in the tournament book.
He says that he was pleased with the opening - and thought he had good chances of an advantage with little risk. Here is his description of the position on move 12:
"At first glance this seems like a completely even position.....Still, a more attentive study of the position shows that white's prospects are preferable. on QN4 it is possible to exchange the bishops on the black squares, after which a comparison of the bishops on Q3 and N2 is clearly in white's favor. Black's queen side is somewhat weakened. The knight on Q2 must guard the K4 square. A summery would suggest that white, in the middle game, is beginning to threaten to take the initiative."
Which I think gives good insight into how Petrosian would evaluate a position - looking at permanent factors; analyzing pairs of pieces, etc.
21.Qe2 is an inaccuracy, and Reshevsky equalizes the game by pushing his a-pawn to a4, solidifying the position of the knight on c4. Petrosian thinks that he should have tried 21.Nc5 Nxb2 22.Bxh7+ Kxh7 23.Qb1+ Kg8 24.Qxb2.
Here is Petrosian's comment to move 25. "Vexed by his inexactness on the 21st move, white is attempting to complicate the position."
Black should have reacted with 25....e5. 25....f5 gives white opportunities for a kingside attack with 26.g4.
Petrosian gives the line 26....fxg4 27.Qxg4 Nxe3 28.Qg6 Nxf1 29.Bf5! but wasn't sure what happened after 29....Ng3 and also had to consider the possibility of 27....Be8.
Petrosian thinks he would have had good practical chances in Reshevsky's time trouble but decided against it - "turning chess into poker and hoping for a 'bluff' is not one of my convictions."
Instead, Petrosian tries to build up his attack deliberately but doesn't get very far.