Quins were depleted due to international duties, but O'Shea was delighted with the job that his stand-in players did.
He reserved special praise for Easter and Brown, the latter of whom was released from the England training camp this weekend.
"Nick is an outstanding leader and Brown reacted phenomenally in the way he played tonight. His involvement in the game was huge. He's absolutely outstanding in the fundamentals of full-back play, he scores tries, he takes responsibility," said O'Shea.
"I hope he gets the opportunity to play at home in a Test match from the start over these next few weeks.
"I'm not saying anything against Ben Foden, who is a great player - injured - and Alex Goode, in outstanding form, but Mike Brown for two years has been absolutely the best full-back in the country."
The win saw Quins return to the summit of the Aviva Premiership.