The Republic of Ireland international, whose form has improved markedly since the turn of the year, had another good game alongside Woodgate and then declared his intention to stay in the team.
"There is going to be a scrap on for places but it can only be good for the club," O’Brien told The Journal.
"Jonathan was under a bit of pressure on Saturday and I am pleased for him because he has come through it well.
"He is a high-profile player and people expected him to walk straight into the team. It is up to the rest of us to make it as difficult as we can for him.
"He's a good player but I'm not going to talk him up too much because this is a dog-eat-dog business. This is what football is about.
"I was disappointed to be left out against Leverkusen but the good thing about this squad is that none of us feel sorry for ourselves. If you get an opportunity, you have to roll up your sleeves and take it."
Meanwhile Sir Bobby has reassured Titus Bramble and Andy Griffin that they are still very much in his plans despite having to settle for a place on the bench against Chelsea.
"People have asked me how I could leave Titus out but I did and we won," he told the Evening Chronicle.
"And what about Andy Griffin? He has been fantastic since he came back. He dipped in the last 10 minutes as we knew he would after being out for nearly a month with an elbow injury.
"But I got two good matches out of him and left him on the bench on Saturday."
"Titus has been magnificent for us lately. And I mean magnificent, although it is not a word I use lightly.
"When I put him on against Chelsea I said to him `you have to pick up the pace straightaway. There is no gradually getting into it. I am putting you on in a pressure situation and you have to be alert all the time' - and he was."