The Argentine found the back of the net at White Hart Lane by wrapping his left foot around his right leg to beat goalkeeper Tomas Kosicky with a rabona shot on the way to a 5-1 victory.
Keown told BBC Sport: "Fantastic skill. I think that's a major self-indulgence to do something like that.
"If it comes off then great but if it doesn't... And if you're watching him play regularly he does overplay a little bit.
"But when he gets the balance right there's definitely a special player there."
Spurs are second in Group C, level on points with Besiktas.