Sussex looked well short of a competitive total when they were restricted to 182 for 8. Their innings revolved around two partnerships, one of 68 in 16 overs for the fourth wicket between Harry Finch and Craig Cachopa and another of 50 for the fifth wicket between Finch and Fynn Hudson-Prentice.
Sussex, who were already out of the competition, experimented with a young line-up, with Hudson-Prentice (20), Christian Davis (23) and Abidine Sakande (21) all coming into the side. Sakande was making his List A debut, while Hudson-Prentice and Davis had played just five previous matches between them at this level.
Almost immediately, Sussex were floundering at 5 for 3 in the fifth over. Matt Coles, generating plenty of pace and bounce from the Cromwell Road end, dismissed both openers in his first two overs.
First Luke Wright, surprised by the bounce, edged behind to Billings, who took the ball one-handed high to his right. In his next over Coles shaped one across the left-handed Wells and Billings again took the catch. Then Davis was athletically caught by Alex Blake at midwicket off Mitchell Claydon for a duck.
But Finch and Cachopa, both cutting well against the shorter delivery, revived the innings until the unlucky Cachopa had his off-stump knocked back by one that kept low from Darren Stevens.
Finch went on to make 54 from 88 balls and Hudson-Prentice scored a stylish 48 off 54 deliveries but there wasn’t much more batting from Sussex as the impressive Coles finished with 4 for 39.
When Kent batted they lost Daniel Bell-Drummond, who was bowled by Ollie Robinson for 14, and Joe Denly, who was given out caught behind off Sakande for 24 after a long consultation between the umpires.
But Northeast, with an unbeaten 66 from 77 deliveries, with five fours and a straight six off Danny Briggs, and Billings, who hit eight fours in a fluent 55, made sure there would no slip-up. When Billings was bowled by Davis they required just another 29 runs and they got home with 12.1 overs to spare.
The Spitfires will now face Yorkshire at home in the Quarter Final on either 17th or 18th of August with the winner awarded a home semi-final against either Northants or Surrey.