It was a bittersweet evening for the 27-year-old who was making his first appearance since shoulder surgery but couldn't prevent an 18-9 defeat to England Saxons in Cork.
The last time O'Brien took to the field in the GUINNESS PRO12 was in Leinster's season-opening defeat at Glasgow.
While he lasted the full 80 minutes on that day he could only muster 51 minutes against the Saxons before being replaced by Eoin McKeon.
But O'Brien insists it was more than enough and is now looking to push on, remaining hopeful of making a return to the Ireland fold for their match with Italy next week.
"I've been out for a while now and there's nothing like game-time to get you back into the swing of things," he told the Irish Times.
"We'll have a look and assess what I've done out there tonight and get working on those things in training this week.
"That's the pleasing thing. That's where I want to be at now. I want to get a run of games. I don't want any more injuries and I'm just happy to be back now.
"I was disappointed to lose the game and I struggled after 20 minutes. I blew up but I was expecting that and overall I was happy just to be back out there and get 50 under my belt.
"Ideally I'd like more game-time before next week but there's no real opportunity between now and then. We'll see what happens now on Sunday."
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