Trump raced into a 4-0 lead with breaks of 114 and 128 putting the reigning world champion in control of the match.
Un-Nooh got on the board with a 73 in the fifth frame, and after a Trump 89 the Thai player reduced the deficit to 5-3 with breaks of 61 and 66.
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However, Trump brushed off hopes of a comeback to win the ninth frame and book a last-four match against Allen on Saturday.
On Thursday, five-time world champion Ronnie O’Sullivan takes on fellow Eurosport pundit Jimmy White, with the winner of that match facing the victor of John Higgins vs Stuart Bingham.
Wednesday’s earlier report
Judd Trump thrashed Stephen Maguire 4-0 in his opening group-stage semi-final match at the Champion of Champions tournament in Coventry.
Reigning world champion and World No 1 Trump raced into a two-frame lead with breaks of 76 and 102, with his opponent managing just four reds in the meantime.
38-year-old Maguire, who was forced to withdraw from the World Open in Shanghai two weeks ago with a fractured ankle, almost pulled a frame back but Trump edged a tight third 69-57.
And three frames down the Scot lost his grip on the match as Trump showed more of the devastating form characteristic of his incredible year, seeing out the match with a break of 68.
Trump will now face either Thailand's Thepchaiya Un-Nooh in the Group Finals of the tournament after he overcame Kyren Wilson.
After losing the opening frame, Un-Nooh moved within a frame of victory thanks to breaks of 63, 51 and 90.
And though Wilson hit back with a 102 and 98 to force a decider, it was Un-Nooh who prevailed with a 69 in the final frame.
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