Clarke hailed another man-of-the-match performance from Lukaku who is on a season-long loan from Chelsea.
Clarke said: "Lukaku is in a really rich vein of form. You could see that with his second goal, when you're playing that well you get a little bit of luck.
"Physically, he's a great specimen, but he has quick feet for a big man.
"It's been good for us, good for Rom, and probably good for Chelsea as well."