In boiling hot weather at Melbourne Stadium, a crowd of 1,651 saw Chelmsford City, who finished third in the regular season, beaten 1-0 by Hampton, while at Princes Park, 1,704 saw Dartford, who only missed winning the title on goal difference, beaten by the same scoreline by Braintree, who finished sixth, a massive 17 points behind the Darts.
In Essex, Chelmsford looked the better of the two sides in the first half and were especially dangerous from set-pieces.
But the Beavers defended well as the half finished goalless.
Then, 8 minutes into the second half came the defining moment of the game when Chelmsford's Jazzi Barnum-Bobb was shown a straight red card for handling the ball on the line.
Max Kretzschmar stepped up and slotted the resulting penalty beyond keeper Jake Jessup to give the Beavers the lead.
Some desperate defending and occasional counter-attacks saw the scoreline remain 1-0 and then the Clarets had a last-gasp chance to take the tie into extra-time, but Elliot Omozusi fired over.
Dartford’s hopes of a return to the National League were dashed, despite only just missing out on automatic promotion to Havant & Waterlooville.
Braintree, who came down from non-League football`s top competition at the end of last season, now have the opportunity to go straight back up after edging this semi-final 1-0.
The only goal of a tight, hard-fought tie came in the 72nd minute when the Darts failed to clear the ball and Billy Crook was on hand to stab the ball into the back of the net.
That proved enough to condemn Tony Burman`s side to a fourth consecutive season in the National League South.