The hosts hit the front in the fifth minute through Christian Benteke, but that was as good as it got for Lambert's charges as they found themselves 3-1 down at the break.
Peter Odemwingie, Peter Crouch and Steven N'Zonzi all found the net before Geoff Cameron added the fourth in the final minute to cap a miserable day for Villa.
It came as a nasty shock to Lambert and the Villa Park faithful, who had witnessed impressive wins over Norwich City and Chelsea in the past two outings, and the Scot felt that the previous week's win over Jose Mourinho's league leaders had taken a lot out of his side.
"Today was going to be a totally different game," he said.
"The euphoria of Chelsea, the game takes care of itself but when you have to beat teams around you it becomes different.
"But that's no excuse, we just never got going. It was unlike us, the whole performance, we looked lethargic and never got going.
"It was just a performance that wasn't like us, the start was great but the goals we lost were really poor.
"We were second best and Stoke deserved to beat us today if I'm honest."
Lambert lost Andreas Weimann and Karim El Ahmadi to injury shortly after the half-hour mark with Villa trailing 2-1, and the manager felt the changes disrupted his team's rhythm.
"The two lads coming off injured probably never helped," he said.
"Andy has a severe dead leg which he couldn't shake off, and Karim we'll have to see, he's got a little strain at the minute.
"It didn't help us because the two lads have been playing really well for us of late and it just upset us a little but that's still no excuse."
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