Trump entered his match against Martin Gould on Friday evening as the bookies' favourite, the Bristolian's devatating early round form making him the man to beat following the exits of Mark Selby and Shaun Murphy earlier in the week.
But he failed to deal with Gould's superb matchplay, the underdog winning three of the last four frames to turn a 3-2 deficit into a 5-4 victory.
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Gould opened up the match with a century break, but Trump won three of the next four frames in an often-scrappy match.
Gould then pinched the sixth frame 59-50 to square the match, and with both players making mistakes he was the man who held his nerve better as he made the semi-finals - thanks in part to a fluked snooker in the decider which helped him on his way.
Former world champion Graeme Dott also made the last-four, demolishing Stephen Maguire 5-1.
Maguire actually claimed the opening frame with a break of 80, but thereafter it was Dott who came out on top in the battle of two Scots - most notably in a sixth frame which summed up the match, Maguire breaking down after putting together a run of 61 and Dott stepping in with a clerance of 71 to claim the match.
Belgian sensation Luca Brecel also made the last four, though his match against Mark Joyce came down to a decider before Brecel claimed it 5-4.
Joyce had actually taken a 4-2 lead after winning three frames in a row, but Brecel hit back with a 79, then pinched the eighth frame 66-52 before knocking in a run of 102 to wrap things up.
In the afternoon session world champion Stuart Bingham was knocked out of the last-16 of the German Masters in Berlin, losing 5-3 to Ryan Day.
Bingham had ridden his luck in his first round match, but was unable to get away with it a second time as Day pounced on a string of errors late in the match to earn a quarter-final against Kyren Wilson.
The world champion started well, making a 76 and a 74 on his way to a 3-2 lead, but world number 18 Day came through strongly, seizing on chances given up by Bingham's mistakes with breaks of 67 and 62 in the closing frames.
“I didn’t score heavily today until the last two frames when I made two good breaks,” said Day, who made the semi-finals in Berlin in 2014.
“I’ve had flaws that have crept into my game over the last couple of seasons but I’ve been working hard on that and my long potting and safety have got better.
"A lot of players of a similar age to me have won tournaments including Stuart and Barry Hawkins so hopefully I’ll be next. I love playing in this venue because the crowds are great.”
Wilson's progress was down to a 5-4 win ver Michael Holt, while world number 44 Mark Joyce beat Mark King 5-2 to earn a match against Luca Brecel, 6-3 conqueror of Norway's Kurt Maflin.
Joyce played some inspiring snooker after losing the opening frame, producing two centuries in the closing moments as he made a ranking event quarter-final for only the third time.
"That’s probably as well as I’ve ever played,” said Joyce. "Mark asked me afterwards if I ever miss a ball!
"I had a new practice room put into my club with a Star table recently and since then I’ve been practising really hard. It’s nice to see the results of that. If play like this someone will have to play well to beat me.”
Friday afternoon session - last 16
Kyren Wilson 5-4 Michael Holt
Ryan Day 5-3 Stuart Bingham
Luca Brecel 5-3 Kurt Maflin
Mark Joyce 5-2 Mark King
Friday evening session - quarter-finals
Graeme Dott 5-1 Stephen Maguire
Martin Gould 5-4 Judd Trump
Luca Brecel 5-4 Mark Joyce
Kyren Wilson 5-4 Ryan Day
Saturday's semi-finals (best of 11 frames)
Graeme Dott v Martin Gould
Luca Brecel v Kyren Wilson
Brecel to face Gould in German Masters final - LIVE on Eurosport
Stuart Bingham: I felt spaced out - I can't believe I won!
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