Trump's eventual win on Saturday opened in even fashion as both players exchanged half-centuries, until Robertson produced a superb 114.
Robertson seized control by consolidating with the fifth frame to move 3-2 up and played the crowd by mimicking cricket strokes in a nod to his Australia closing in on a 2-0 lead in the Ashes.
But this Australian couldn't press on as Trump surged back, winning four straight frames on the back of half-centuries.
A last break of 53 confirmed his place in a fifth career UK Championship final and a chance to retain his crown.
"Another final," Trump reflected afterwards. "So it's been a good end to this calendar year, really, after quite a poor midseason. I'm happy to have another shot at it.
"It's not been brilliant the whole tournament. I'd love to play better, but at the moment I haven't really needed to."
Selby sets up Trump showdown
Awaiting Trump in Sunday's final is Mark Selby, who beat Shaun Murphy 6-3 in Saturday's second semi-final.
Selby produced a series of high-quality breaks, including a classy 127 to secure the victory.
Murphy staged a comeback, registering a century of his own, but Selby’s composure and tactical nous proved decisive.
"I'm gutted to have lost," said Murphy afterwards. "Nobody comes for second place. I suppose a lot of players would've swapped with me. I've had a great week.
"I could've lost to John Higgins... I should've been on the way home. It was a great match. I don't think I did a lot wrong, I thought Mark was superb."