Bowen is a great defender. But to control Nash, they had a team concept that functioned in a very disciplined way. And they managed that by having Bowen constantly bump and grab Nash to gain the little time for the help defense to reconfigure. Then, Bowen would catch up with Nash again. They rarely fell into the trap most teams constantly fall in the regular season, which is to get completely confused when Nash dribbles past one or two defenders in the paint.
Often, only late in games when the opponents get tired and the concentration vanished a bit we seem to be able to find some "open" looks, mainly via Amare's energetic drives and cuts. In game 5, the refs started the game by calling it close on the Spurs, which jump-started the Suns-style offense a bit. But later in the game, they went back to the normal way and we were too tired, blame DA for that, to execute.
Also, DA made sure with how he handled the roster and regular season games that once Nash is neutralized like that we don't have sustainable alternative offense to still win the game.