Villa had come back from a goal down and had a strong foothold in the game when Shelvey's goal from the centre circle put the Swans back in front at 2-1 midway through the first half.
"Brad Guzan has been fabulous for me in the two years that I've been here so I'm not going to criticise that lad for that," said Lambert.
"He'll make saves again to keep everybody safe on that front. But the second goal was a major turning point in the game."
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