O'Brien scored the penultimate try for the Lions at the Hunter Stadium and knows there are few chances left to make an impression before the long awaited Test series against the Qantas Wallabies kicks-off in Brisbane next week.
"I think lads know it's coming closer and closer to the Tests and that gets you excited and keeps you on your toes. You're trying to push on and we're trying to develop and improve every week," said O'Brien.
"We set ourselves a standard from the first game, moved on to the second one and then the Reds game - and so on and so on. We're trying to build and build to get the complete package.
"We set ourselves standards over the last couple of weeks and we want to maintain those. We probably went away from the game-plan a little bit in Newcastle, and we were a little bit sloppy in certain areas, but overall we'll look back and we played well enough.
"We did our jobs, but there is stuff to work on - as there is every week. There was some good stuff in it and obviously some stuff we need to work on as well.
"We were a little sloppy at times, so that's a little bit disappointing but, overall very, very happy with the result. We made life difficult for ourselves at times in the second half - a couple of handling errors, just being a bit sloppy and going away from the game-plan.
"Other than that there were some nice passages of play and we put together some nice phases at times and scored some great tries. I think that's the big point, we're getting used to ach other.
"Obviously, there are different combinations every week, but as a group we're gelling together a little better and that's gradually building and building and, hopefully, over the next week or two we'll have that finished off."
Next up for the Lions are the Waratahs, a team coached by O'Brien's former mentor at Leinster, Michael Cheika. So what is he expecting from his former coach and his new side?
"We're getting closer and closer to the Test games and teams are going to try and come at us a little bit harder. The Waratahs will be no different," he added.
"It's going to be a very tough game and, whatever side is picked for the Lions, we're going to have our hands full at the start of the game again. They're really going to come at us out of the blocks and try and hurt us a little bit so it's going to be massively intense again.
"I know Cheiks very well and he's an animated character. I'm sure he'll have them fired up and wanting to be really aggressive and come hard at us."