The Albion defender enraged his boss Steve Clarke when he was sent off for spitting on Tottenham right back Kyle Walker.
And Villas-Boas echoed Clarke's sentiments and praised Walker for not reacting to the incident.
He said: "It's difficult for the ref, but Popov did what he did and Walker did nothing to react.
"It's difficult to assess but I think Mark Clattenburg made the right decision. It's horrible and nasty."
Tottenham have collected four points from two away games at Norwich and West Bromwich in the space of four days, and Villas-Boas is delighted with the return.
"It has been a very important week for us," The Spurs manager added. "To get four points away from home, with not much time between the games, is excellent.
"We have put ourselves in a very good position to threaten for third place."