Lock O'Connell needs surgery on his damaged hand and is expected to be out for another month while hooker Sheahan damaged neck ligaments at the weekend.
Ireland put in a remarkable 99 tackles, missing just one, and lock O'Connell said he felt both sides played as if they wanted to make amends for their most recent performances.
The visitors had prop Paul James sin-binned for 10 minutes after infringing at a huge Munster scrum and soon after Munster received a further boost with the introduction of Ireland and Lions lock O'Connell.