Dreams of an Iffley swansong for Lincoln’s 2010 Cuppers winners were dashed with a brace from Wadham’s Jeremy Stothart.
The midfield general nodded the decider deep into extra time having pulled his side level with a similar goal from a set piece early in the second half.
Lincoln, who secured a 1-0 victory against their opponents in the league last term, had taken an early lead when Torsten Alexander nodded home from Nathan Riddell’s catapulted throw.
Their opening goal was just reward for a half of intense pressure. Wadham struggled to deal with the aerial threat of right back Sam Townsend, who twice went close before the break from Alex Biggs corners.
But Wadham could have netted an equaliser just before half time when diminutive winger Chris Nicholls fired high and wide after being put clean through.
A first half of free-flowing, end-to-end action was followed by a scrappier affair in which Wadham deservedly forced an additional half hour.
Lincoln shot stopper Rob Kelly continued his imperious form from the quarter finals, saving low to deny Vivian and lone striker Chris Wright. However the Scotsman was powerless to deny Stothart’s header from the resulting corner.
Lincoln looked the sharper of the two sides in extra time but could not force a winner with Ben Szreter imperious between the sticks.
Substitute Alex Wilson saw his low effort smothered shortly after the restart following strong work from stand-in skipper Alex West to regain the ball on the byline.
Yet Stothart delivered the sucker punch in the second fifteen, towering above a packed penalty area to set up a final with holders Worcester.