I think finding himself a shot behind was the best thing that happened to Spieth all day. The pressure of leading the Open seemed all to much for him, and as soon as he'd appeared to have thrown it away, the pressure was off and the very next hole he nearly gets a hole in one. That kick started him into top gear, and he played unbelievable for the last 5 holes.
What is worrying for the rest of the golfing world, is the confidence this now gives Spieth moving forward in these major championships. What happened with Spieth today is probably the biggest test of a golfers temperament that you'll ever see, and in 99% of cases the player would have completely imploded from the 12th hole onwards. I've seen it so many times when a player throws away a lead like that in a major, they just fall apart.
This is just going to make Spieth feel even more comfortable when in contention for a major, as even when things start to go wrong he now knows he has it in him to turn things around.
I wouldn't be at all suprised to see him complete the career grand slam next month at the PGA. Il definitely be having another punt on him in that tournament.