The Spurs won Game 5 against the Rockets in overtime after riding some big time play from Danny Green.
James Harden failed to show up in overtime and had a potential game tying three pointer blocked by 39 year old Manu Ginobli. It could be that Harden was tired due to the fact that the Rockets only played 7 players in the game.
It could also be that Harden just isn't a clutch player. Maybe more of a regular season kind of guy.