The rejuvenated Welshman - playing with a new cue - did not offer his Group B rival Trump much of a chance as breaks of 122, 107 and 60 saw him pick up three points with minimal fuss at the Marshall Arena.
It is difficult to believe world number 36 Day - nicknamed 'Dynamite' - had not beaten a top-64 player this season until this week as he topped the table on five points with some serious sparkle and two 2-2 draws with the heavy-scoring David Gilbert and Barry Hawkins.
"I was really pleased with the way I played all day," said Day, who turned 40 on 23 March. "It doesn't get tougher than against Judd. It was a good draw with Dave and I was delighted to get the frame I needed against Barry.
"I don't know whether it is being in the zone or whatever they call it, I felt great all day.
"I just played lovely. It's been a long time since anyone has played competitive snooker and I think the break might have done me a bit of good, give me a bit of a boost.
"The lockdown has helped me, and I'm looking forward to the final."
He rolled in his third ton of the day in contributing 103 against Gilbert in the opening frame of his second match with last year's World Championship semi-finalist.
Gilbert produced a fine 117 in earning a 2-2 draw with Day.
The standard was electric with Gilbert drawing 2-2 with Hawkins, who finished with a 130 break after his opponent had ran in 59 and 64.
Trump - who made 51, 59 and 60 in his final two group games - collected his first win of the day with a 3-1 success against 2013 world finalist Hawkins, but saw his tournament hopes ended by Gilbert in a 2-2 draw.
Gilbert was on for a 147 in the fourth frame, but could not pot a tough final yellow after doubling the final red to keep the break alive.
Day just needed one frame against Hawkins to ensure his progress to the final and wrapped it up with a 62 break in the opening frame and a 61 in the third.
Hawkins showed his class with two glorious contributions of his own, a 114 break in the second frame and a timely 89 to earn a 2-2 draw.
Day joins 2015 world champion Stuart Bingham, Ben Woollaston and Luca Brecel in the final group on Thursday.
Belgium's leading player Brecel topped Group A on five ponts with a 3-1 win over Ashley Carty and two 2-2 draws against Mark Joyce and Gary Wilson.
Brecel lost the third frame to Joyce on the three-shot miss rule, but hit back with runs of 109, 64 and 74 in his 3-1 win over world number 83 Carty.
Carty required a victory over Joyce in his final group game to qualify, but lost 3-1.