The winger's heavy first touch looked to have narrowed the angle with Pernis rushing from his line, but he slipped a delicate right-footed reverseshot into the corner of the net.
The Chelsea defence was caught square as Harewood latched onto a cute reverse ball from Reo-Coker and was able to follow-up his own shot that bounced following a save by Petr Cech.
The Republic of Ireland Under-21 international sent a magnificent reverse pass into the inside-right channel for James McArthur to run on to but the midfielder's shot was too weak and was held by Olejnik.