Rugby suffered an Easter Monday defeat in their first trip to the Banbury-based club for their penultimate game of the season.
Valley had led at the interval thanks to Caine Elliott's ninth goal of the season just ahead of half-time, but they let the hosts back into the game by gifting them an equaliser shortly after the restart before conceding again in the 72nd minute.
There was a change in formation and one change to Town's starting personnel with the return of skipper Loyiso Recci to the side as part of a central defensive three at Addison Road, but it was the home side that made the better start to the game, with Andrew Stidder drawing a fine save from Ash Bodycote in the early exchanges when he was through on goal.
Stidder had a further chance which he blazed over, after Barry Fitzharris had initially done well to thwart Luke Swann with a good saving tackle.
Justin Marsden's strike over the bar represented a rare opening for the visitors, although Town did then start to make an impression with both Madundo Semahimbo and then David Kolodynski shooting high of the target.
Elliott's opener came on the back of an excellent team move from Rugby, with James Hancocks first dispatching a diagonal crossfield pass to Kolodynski, who controlled the ball smartly before laying it into the path of Marsden for a first time effort which Easington keeper Dale Freeman did well push away.
However the ball looped up nicely in front of Elliott to apply a nicely controlled volley into the back of the net.
Valley nearly added a second before the break, when Recci whipped-in a dangerous cross which Semahimbo just failed to connect to with his head - allowing Freeman to punch clear to safety.
Sports were level within two minutes of the new half though when Bodycote passed straight to Alfie Dunn, and the striker took full advantage of the error to calmly round the keeper and stroke the ball over the line.
Dunn blazed one over shortly after, whilst Hancocks's shot from twenty yards also missed the target as Town looked to regain the lead.
Hancocks then tested Freeman with a decently low struck free-kick, with Semahimbo blasting his strike straight at his own man in the next phase of play.
Semahimbo was soon back in the action when he battled back the ball on the edge of the box to set up a good chance for Elliott, but this time his lifted effort was plucked out of the air by Freeman.
The winning goal came after Adam Taylor released Luke Swann down the right hand channel, and the Easington skipper took the ball on before firing home a low shot into the bottom corner.
Rugby tried to get back on level terms in the remaining twenty minutes, but too often lacked conviction in their attacking play.
Their best opportunities to equalise came when Recci's header to a Hancocks corner was cleared away on the line and when Kolodynski's first-time volley from the edge of the penalty area flew just over.
Rugby line-up: Bodycote, Summerfield (Ahenkorah), Hancocks, Francis, Recci, Clarke, Fitzharris, Elliott, Kolodynski, Marsden (Shaw), Semahimbo. Subs not used: Lock, English
Valley Line-up: Bodycote; Recci, Clarke, Francis; Summerfield (Ahenkorah), Hancocks, Fitzharris, Marsden (Shaw), Elliott; Semahimbo, Kolodynski. Subs not used: Recci, Thomas, Francis, Lock, Ahenkorah. Booked: None.
Easington line-up: Freeman, Sherpa-Moore, Haynes, Rose, O'Regan, Smith, Swann, Eyre, Stidder, Taylor, Dunn. Subs: Gueye, Stott, Butler, Fountain.