Amator Cup 2012-11 Rd7

I played an uneventful looking quick draw today and now stand at 4.5/7. However, the analysis shows many subtle points that I was blissfully unaware of during the game.

The other four games had plenty of life in them.
Nagy,L-Molnar 0-1
all other games were still in progress when I left.

Here's the game.

Yip,M (2085) - Zilahi,G (1940)
Slav ...a6 5.a4[D15]

Amator Cup (7), 22.11.2012
Black chose the fashionable solid ...a6 Slav and white showed no real understanding and insufficient preparation and understanding to make any headway. In the even ending that followed there was a moment for white to show some level of competance. Here it is.

Critical Position

The b- pawn is under attack. How should white react?

White to Play