Twice it has looked as if The Rocket was going to take the match away from his young Grove scholar and twice the Bristolian has found a way to hold onto the defending champion's coattails.
In the first session, Trump was 4-1 behind and struggling to score as easily as O'Sullivan. It looked even at this early stage of the encounter as though he would hit Trump hard and quickly assume control, but he won the last three frames and levelled overnight.
|Picture by Monique Limbos|
The second session looked much the same. After sharing the first four frames, O'Sullivan rattled off three in a row and had Trump on the back foot again at 9-6. Trump was not dettered again and won a tense finalframe to end up 9-7 instead of 10-6.
Trump wasn't anywhere near his best and looked to suffer again from a lacklustre morning performance but the worry here is that he may have missed a golden chance to stride towards a place in his second Crucible final.
O'Sullivan admitted after beating Stuart Bingham that it takes at least one, maybe even two sessions, to adapt to the one table format. His theory has been proved true. He has been playing in his lowest gears so far yet Trump has looked nervous and only managed to keep himself in the contest, rather than taking the chance to open a lead.
I'm not writing Trump off. Far from it. I'm sure he will come out and play better in the second half of the match and showed his courage to come back against Shaun Murphy in the last round, but O'Sullivan is going to get better as well.
Trump needs to take the match by the scruff of its neck and put into practice what he vowed to do in his press conference. He threatened to attack O'Sullivan, put him under pressure and scare him on the table. So far, this kind of performance hasn't materialised.
O'Sullivan has shown glimpses of brilliance in this tournament but hasn't found the consistency he did here when he won the title a year ago.
The four-time champion hasn't trailed a match here yet and is closing in on the final without really having been pushed to the fullest.
Trump has everything he needs to rattle Ronnie. At the halfway stage of this match, it's time for him to push on and exploit any of O'Sullivan's vulnerability.
He might not get the chance to face the master again at the World Championship. He needs to seize the moment.