Holders Durham's hopes of reaching a second consecutive Lord's final depend on a colossal performance with the bat after Kent - put in after Durham won the toss - topped 300 in their 50 overs at the Riverside.
Martin van Jaarsveld, their prolific South African batsman, led the way with his fourth century in this season's competition, finishing unbeaten on 122 after hitting three sixes and nine fours.
His latest feat comes only days after he struck two hundreds and took five wickets in an innings against Surrey in the County Championship.
There was a century too from the young Englishman, Joe Denly, whose 102 contained 15 fours, although he had some luck along the way, being dropped on 37 and twice almost playing the ball into his own stumps.
Steve Harmison bowled superbly for the home side, the England paceman regularly hitting the pitch at 90mph-plus and taking four wickets.
Harmison had England man Rob Key caught behind with a beautiful late out-swinger to break an opening partnership of 96 and bowled Denly, Azhar Mahmood and Justin Kemp to finish with 4-47 from 10 overs, his best figures for Durham in one-day cricket since 2003.
England colleague Liam Plunkett also bowled impressively, conceding only 36 runs off his 10 overs, in contrast to South African Albie Morkel, whose seven overs went for 75.
After the heartbreak of missing last year's final through injury, Harmison may miss out again unless Michael di Venuto, Dale Benkenstein and company can produce something special in replay.
There was a surprise appearance in the match by England's one-day captain, Paul Collingwood, who asked to be allowed to play after originally being ordered to rest ahead of next week's first Test against South Africa.
His contribution so far, however, has been to send down just one over - at a cost of 14 runs.