The third change was not enforced by injury problems, though, as London Irish star Justin Bishop replaced Munster's John Kelly on the right wing to mark his return to the side after suffering a broken hand.
It is a blow for Kelly who had played well against both Italy and France and O'Sullivan said: "It was a difficult decision to bring Justin in ahead of John. They are both quality players.
"We called it for this game because we think Justin is the man for this particular job. I just think he's the right person to play on the wing against Wales. The opposition was a consideration."