O'Connell was man of the match as Munster produced a devastating second-half performance to down the English champions, with veteran fly-half Ronan O'Gara kicking all the points.
Munster coach Rob Penney said: "He hasn't played a lot recently and he will get better with more game-time. I suspect that by late June and early July, he will be humming."
He added: "He is great isn't it? Everyone speaks about him in glowing terms and so they should. First and foremost he is a wonderful man.
"He has this empathetic outlook on life, he sees things through other people's eyes, and he has this understanding that makes everyone feel good to be around him. You couple that with his rugby ability and he is just a really complete man. Munster have fed off him for a long period off him."
Harlequins led 9-6 at the interval after enjoying early dominance in the scrum but they began to lose shape and composure in the second half as Munster turned the screw.
"The better side won," O'Shea admitted. "The won the breakdowns and the collisions and we are bitterly disappointed.
"We have to take a bit of time but I said to the guys that they have to learn from the journey that Munster went on (before winning their first Heineken Cup title).
"Sometimes you are driven by that hurt. We did not play the way we could today. We were not allowed to play because Munster bossed the second half.
"I thought Paul O'Connell was absolutely majestic. The whole team was physical but he was the totem that the whole team just rose around."
- Sports & Recreation