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Dover made an immediate return to National League South on Monday after winning a tense play-off final at Dartford.
Second-half goals from Ruben Soares-Junior and Alfie Matthews ensured Jake Leberl's team bounced back at the first attempt after last year's relegation.
But Dartford will remain in Isthmian Premier after failing to find a way through an excellent Dover defence.
The windy conditions and below-par playing surface meant it was never likely to be a classic on a bitterly cold afternoon at Princes Park.
The teams shared 10 goals in their two league games but this was always likely to be a tense affair with so much on the line.
Dartford sent a first-minute header over from a Samir Carruthers corner and settled the quickest of the two sides. An imaginative 20-yard chip by Carruthers on 14 minutes landed on the roof of the net.
The major talking point came as early as the 16th minute with virtually Dover's first attack of the half. George Whitefield was adjudged to have fouled Luke Baptiste as he latched onto a ball over the top of the Darts defence.
Having given the foul, Whitefield must have feared the worst but referee Luke Scott only showed him a yellow card, presumably thinking that Baptiste was heading away from goal having got to the ball first. Dover's protests suggested they didn't agree with that call.
Matthews, who scored two free-kicks to see Whites through their semi-final tie with Billericay in extra-time on Wednesday, stepped up but shot straight at keeper Jacob Marsden from 20 yards. It was Dover's only attempt on goal in the first half.
Callum Jones, passed fit despite a back injury, exchanged well with Olly Box before his right-foot shot was blocked.
Not for the first time this season, Darts midfielder Denzelle Olopade was catching the eye with an all-round display and he fed Box on 30 minutes but his right-foot shot from 20 yards lacked power to trouble keeper Mitch Walker.
Jones then dug out a cross for Box but he was denied by some more brave Dover defending.
Darts forward Jones had largely been kept in check but he turned Joe Tennent on the halfway line, only for the Dover defender to get back impressively and block his attempted cross to the unmarked Box.
Fuad Sesay was caught out as he tried to bring the ball out of defence for Dover just before half-time but Carruthers shot well over the bar as the teams went in goalless.
After the break, both Matthews and Dartford's Sam Odaudu avoided yellow cards with referee Mr Scott continuing his lenient approach to the game.
The breakthrough arrived on 57 minutes. George Nikaj was fouled in the box and Soares-Junior must have been the coolest man in Princes Park as he beat Marsden with a Panenka to put Dover ahead from the penalty spot.
Dartford never really got going in response. Every time Box or Jones got the slightest sight of goal, Dover's excellent defence closed the space down in an instant. Centre-backs Jacob Mensah and Luca Cocoracchio barely put a foot wrong. Darts boss Ady Pennock turned to Eddie Dsane in a bid to get them back on level terms.
Matthews sent a long-range free-kick wide for Dover with eight minutes left before Dartford immediately responded as Box advanced before keeper Walker beat away his fierce 30-yard piledriver.
Then Jones played in Hayden Bullas but he failed to lift his shot over the advancing Walker, who was out smartly to make a low save.
Box went down too easily in the box, with the referee perfectly positioned to turn down Dartford's penalty appeals. The visitors broke down the other end with Marsden cautioned after racing out his goal to bring down Soares-Junior near the touchline.
Dover delivered the ultimate punishment when the 88th-minute free-kick was only cleared to the on-rushing Matthews, who expertly directed his header in off the far post, to put Dover on the verge of promotion.
They had just six minutes of stoppage time to see out with the 600 travelling supporters in dreamland.
Dartford: Marsden, Hill, Whitefield (Dunne 88mins), Olarewaju (Williams 62mins) Okoye (Pinder 74mins), Olopade, Carruthers (Dsane 74mins), Bullas, Odaudu, Box, Jones. Subs not used: Christian-Law, Dunne.
Dover: Walker, Charles-Cook, Tennant, Mensah, Sesay, Cocoracchio, Matthews (Gyebi 90mins), Hanson, Nikaj (Lucan 90+4mins), Soares-Junior (E Angbaduba 90+5mins), Baptiste. Subs not used: T Amgbaduba, Mampolo.
Referee: Luke Scott.
Attendance: 3,805.