With only nine minutes on the clock Ricky Holmes burst into the box to put the home side ahead, but Matt Harrold headed home soon after half-time before O'Brien ensured the scores stayed level with a string of saves from Harrold, Eliot Richards and Wayne Brown.
Robson said: "Liam was outstanding and he made a lot of very good saves for us. He can be really pleased with his performance. Hopefully he can take some confidence from that into the next game.
"It was a good point in the end because it gets us up and running - and that's exactly what we needed after Saturday.
"I can't fault their attitude and commitment to the cause. They're a great bunch of lads who want to fight for each other. That team spirit will go a long way throughout the season.
"We've got it in abundance and I'm sure we can only get better. There was lots to be positive about in the first half and if we can do it for 90 minutes it will be difficult for teams to come here and get something."