jith1207: I don't understand why white doesn't have escape route for the queen at 28th move, I don't see a problem with queen to f3 or g3.
I was watching live with Silicon analysis and I always have messed up when opponent has a passed pawn in my games so I was hoping to see how to defend such end games. It looked to me that Yeoh was confident of advancing the passed pawn to queen, the only reason I could think of sacrificing the queen earlier. So this idea was the highlight : in order to break a passed pawn with only a valuable force such as queen at disposal, which you can't always use to block and afford to lose for the fear of knight making it move away or other passed pawn progress as in this position, the key was to make opponent block the rook and pawn by the opponent's own knight!! Then the queen gets between the pawn and knight, pinning the rook which makes easier grabbing the passed pawn. As I am typing now, I recall Anand deployed same tactic in one of the very most awe-striking games played by Vishy ever (I forgot whom he played against).
This can be done in this position because queen is attacking the other white pawn which can free Black's own passed pawn on the 'a' file. In order for the queen to attack, she has to move and his only other blockade available, the king, needs to come closer. And that's the reason for the urgency of move Kf7 in the move 46. It's amazing how quick the grand masters recognize such positions and tactics and the utility of resources at hand and execute them all at correct moment (as I was watching, Anand seemed to concur with the idea of computers, even though many of the moves he played after move 40 are the "only" moves that do not end up in draw, Kf7 being one). That's high quality chess for me!