Lukaku scored a first-half penalty before charging down a Simon Mignolet clearance that rebounded into the net to make the score 2-0.
The striker was easily the best player on the pitch, with his strength, power and pace continuously causing Sunderland's defenders problems, and Clarke admitted that he was the sort of forward he would not want to face.
"He's in a great run of form and has done really well for us," Clarke said.
"He [Lukaku] had a partner up front with him today which helped him. It gave him space to make the runs in behind defenders that he likes to make.
"As a former defender I certainly wouldn't like to face up to him."
Clarke also commented on Lukaku's second goal, a fluke after a charged clearance from Simon Mignolet rebounded off the on-loan forward and into the net.
"Yes it's luck. But it's also good endeavour. He could have given it up, let it run through to the goalkeeper and given him an easy clearance. But he chose to chase it down.
"Normally when that happens it goes wide but it went into the net like a bullet.
"That probably tells you how he [Lukaku] is playing at the moment, but when you are playing well it goes in."