Reigning champion Trump lost a dramatic encounter with Kyren Wilson that lasted the distance in the second round.
Wilson led last week’s German Masters winner 3-1 but back came the world number one to restore parity and force a deciding frame.
A subsequent break of 50 from Trump appeared to give him the ascendancy but, after a long tactical battle, Wilson prevailed when potting the final pink.
Meanwhile, O’Sullivan fell at the quarter-final hurdle courtesy of a 5-3 reverse to Scotland’s Graeme Dott.
The “Rocket”, who was one of the front-runners with Betway, also trailed 3-1 before a break of 102 helped him to retrieve the deficit as well.
However, O’Sullivan paid the price for fouling when in among the balls in the seventh frame as Dott regained the advantage, before a break of 91 completed the upset.
O’Sullivan’s wait for a record-breaking 37th ranking title goes on, and he’s yet to capture a trophy of such status this season so far.
For Dott, the 2006 world champion has qualified for the semi-finals of an event for a second successive week and is impressively maintaining his efforts to return to the elite top 16 in the world rankings.
The 42 year-old faces Tom Ford in the last four so a somewhat unexpected finalist is guaranteed.
Ford, who also reached the semi-finals of the English Open earlier this term, overcame Gary Wilson 5-2 – helped by tallies of 84, 69, and 54.
There are still a couple of World Grand Prix favourites left in the hunt in the top half of the draw, though.
Neil Robertson’s incredible hot streak shows few signs of dwindling as the Australian returns to the business end of a competition for the third week on the trot.
The European Masters champion appeared a little tired in his final defeat to Trump in Berlin on Sunday.
Yet, a hat-trick of century breaks in powering past Mark Williams suggests that Robertson is doing just fine after all.
The 37 year-old meets close pal Joe Perry in the first session on Friday as the quarter-finals are completed at the Centaur.
Robertson, who has risen back to world number two in the rankings, is 13/8 with Betway to seal a second success of 2020 already.
Four-time world champion John Higgins is the remaining competitor still in contention, with the “Wizard of Wishaw” in action against Wilson.