Gateshead trailed 2-0 at the Silverlake but they pulled it back with two minutes to go yet were sucker punched late on - watch match highlights here.
Jordan Preston and Vassell equalised in the final three minutes after Ben Williamson and James Constable put the home side in front.
But Ben Strevens won it with the last kick of the game.
"It's an extremely disappointing result for everyone," said Vassell. "We put ourselves in a difficult position at 2-0 down but we did well to come back into the game but we just threw it away right at the end.
"I though we could have done better for all three goals we conceded. We were sloppy and paid the price.
"There are positives that we showed fight to get it back to 2-2 so late on but obviously the big, all important negative is the fact that we lost right at the end.
"It was my mistake for the first goal so I thought I'd atoned for it by scoring a late equaliser but it wasn't to be."
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