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Maidstone conceded an injury-time equaliser for the second game running - this one scored by a right-back playing in goal.
Stones looked set to take top spot in the Ryman League Premier Division until Joe Gatting, acting as a stand-in keeper with Peacehaven's regular away in Canada, levelled with a penalty.
United found their new targetman in the absence of Jay May - centre-half Steve Watt.
The Stones captain - who became a dad for the second time before Christmas - was pushed up front alongside Frannie Collin and Alex Akrofi in a switch to 4-3-3.
It was a system that suited Watt in that he won his headers and made a nuisance of himself while having others around him to do the running.
Stones took the lead after just 56 seconds with Akrofi getting the final touch on the line after James Rogers' long throw led to a goalmouth scramble.
Akrofi didn't give defenders a moment's peace and went closest to a second goal before half-time, collecting Collin's pass, shaking off Dan McLaughlin and bending an effort towards the far corner that was touched wide by Joe Gatting.
Peacehaven had their moments on the break with Trevor McReade firing over after a long ball caught out Sonny Miles and Jamie Coyle.
Tom Burton might have done better with a header from a free-kick - he was perhaps surprised the ball reached him - while late in the first half Phil Starkey and Chris Piper combined to play in Alex Brown whose strike went inches over.
Brown twice threatened early in the second half before McReade wasted a golden chance for the equaliser, clearing the bar when played in by Burton.
It triggered a decent spell for the hosts with United having to defend well during a disjointed period for Jay Saunders' men.
Peacehaven, winners at Margate last week, were comfortably the better side after the break and got their rewards from the spot following a foul in the area.
Maidstone: Worgan, Starkey, Mills, Coyle, Miles, Rogers, Piper (Greenhalgh 79mins), Watt, Akrofi (Bodkin 64mins), Collin, Brown. Subs not used: Simpson, Jordan, Godmon. Attendance: 746.