There were 12 seconds between Vine and Yates in the prologue, and 11 in the end: there was no other stage when there was time between them. It was very much decisive.
But that doesn't necessarily mean that Yates would have won the race by one second without the prologue. Perhaps the last stage proved to be a bit too easy, but I still think the route offered opportunities for riders to make up their deficit after the prologue.