McLeod - the oldest player at the Crucible Theatre aged 46 from Wellingborough - was 1,000-1 for the title before the tournament began, and recovered from trailing 4-0 to win 10 of the next 14 frames in what was the biggest win of his 26-year career.
McLeod will face Scotland's Stephen Maguire over the best-of-25 frames in the last 16 for a quarter-final place.
"It's brilliant. I was relaxed at 4-0. He was potting everything. There is not much you can do so you have to bide your time," said McLeod on the BBC.
"Maybe I went into zombie mode because I didn't know the score..if it was 4-4 or 5-4.
"I tried not to think about things too much. You have to dismiss the pressure."
Trump - world number two and 4-1 pre-tournament favourite alongside defending champion Mark Selby arriving in Sheffield - had appeared to be struggling with a shoulder injury as he resumed 5-4 behind on Wednesday morning.
He faces a small fine from World Snooker for failing to speak to the media afterwards. Understandable given the circumstances, but McLeod believes the shoulder injury cannot be used as an excuse for Trump again coming up short.
"He was 4-0 up and he didn't look that injured, so what can I do?" said the man nicknamed 'The Highlander' after the lead character from the 1980s film.
Read the full article on eurosport.co.uk: 1,000-1 outsider McLeod stuns Trump in huge Crucible upset