Originals rose to the pressure of a must-win game by totalling 154 for six and then bowling and fielding brilliantly to bowl the home side out for just 75.
The defeat, in front of a bumper 21,00 crowd, denied Phoenix a win which would have virtually sealed their passage.
Both sides now have it all to play for in their final games, Phoenix away to London Spirit on Tuesday and Originals at home to Oval Invincibles on Wednesday.
Originals chose to bat and only Phil Salt 56 (38 balls) passed 30 against an attack led by Benny Howell (three for 18) and Kane Richardson (two for 27).
That total looked no more than par but Phoenix's chase started badly, with two wickets in the first four balls by spinner Tom Hartlety, and never recovered.
Hartley finished with four for 22 as the Phoenix challenge fizzled out after just 74 balls.
Originals started their innings solidly, reaching 50 from 38 balls for the loss of only Laurie Evans, who skied a slog at Richardson.
Salt charged to a 33-ball half-century much to the angst of Henry Brookes, who dropped him at short fine leg on eight and was then lifted for two sixes in three balls as the batter charged straight through the forties to his fifty.
The consistent Howell kept a brake on as Wayne Madsen, Tristan Stubbs and Paul Walter all fell flailing against the medium-pacer.
All sent up skiers before Salt's assault was ended by an lbw decision for Richardson, the batsman departing in high dudgeon after being told that his call for a review, which would have been upheld, arrived too late.
At 113 for five from 82 balls, the Originals needed a late rally and Tom Lammonby supplied it with a meaty 12-ball 26 including four fours and a six.
Hartley then struck two immediate hammer-blows on the Phoenix chase. From the spinner's second ball, Miles Hammond was caught at extra cover. His fourth bowled skipper Moeen Ali through a slog sweep.
Sneed and Chris Benjamin partially rebuilt with a stand of 45 in 31 balls but both fell in the space of three balls. Benjamin was run out by Madsen's direct hit and Smeed hoisted Paul Walter to deep square leg.
Hartley returned to remove Brett D'Oliveira, caught in the deep, and bowl Ben Dwarshuis which left the Phoenix in a heap at 63 for seven, doomed to an ignominious defeat and needing to lift themselves very quickly for the vital visit to Spirit on Tuesday.