O'Neill, 59, was appointed as manager of Sunderland just over a month ago and handed McClean a rare chance in the first team soon after.
Subsequent promising performances have resulted in McClean's continued selection, and O'Neill is hopeful that the striker can continue his good form into the new year.
"I couldn't be more pleased with him. He has come in and he has been exceptional," said the Sunderland boss.
"He came on in the game when perhaps maybe we seemed to be chasing lost causes against Blackburn and lit the place up.
"His emergence has been fantastic."
McClean joined Sunderland from Derry City for a fee of £350,000.