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Welling missed the chance to go top of Blue Square Bet South when they lost 2-1 at in-form Sutton on Tuesday night.
Wings - who would have gone top on goal difference with a victory - felt they should have had an early penalty following a challenge on player-manager Jamie Day.
But Sutton were the better side and forced a number of saves from Sam Mott, pictured, who also kept out a Sam Rents penalty on the stroke of half-time.
United finally went ahead on the hour as Craig Dundas met a cross from the right.
And they doubled their advantage five minutes later when another cross from the right was finished by Harry Ottaway.
Welling pulled a goal back two minutes from time with substitute John Main setting up Ross Lafayette.