The 33-year-old had been out of action since October with a back injury, but could yet be fit to join the Lions squad this summer.
"I'm delighted to be back and right now not feeling any ill effects. I'm happy with the way things went, although I was finding it tough towards the end - but I suppose that's to be expected if I'm trying to keep up with these young fellas," he told Sky Sports News.
"I'm injury free but I don't know about fit. It was very enjoyable. The lads played some great rugby. Luckily enough, it was a great day, a dry ball and that makes it harder on the lungs which is exactly what I needed."
O'Connell has made 85 appearances for his country.