The Republic of Ireland international was given his first taste of pre-season match action when he came on as a half-time substitute for Guy Demel.
"It was good to get a run out," O'Brien told whufc.com. "I've been training hard the past few weeks so it was nice to get the run out and get some minutes under my belt.
"It's been a gradual build up for me. I've been training hard but I just didn't feature in the first two games. I started on Saturday with my first 45 minutes and hopefully I'll get some more on Tuesday night. It's going cool."