Luke Varney signed off his Owls loan stint in style, bagging both goals of an entertaining game to all but condemn Southampton to League One.
Varney, who now heads back to parent club Derby following the end of his temporary spell north, scored either side of half time to hand Wednesday three fully merited points.
For Saints, the defeat will almost certainly prove devastating as they now seem destined to tumble out of the Championship and into the next tier down.
The Owls made two changes from the side that lost at QPR on Easter Monday, with James O'Connor making way for Sean McAllister in midfield, while Francis Jeffers returned up front in place of Leon Clarke.
Wednesday started brightly as Southampton struggled to get the ball out of their own half in the first ten minutes. Jeffers and Varney looked lively and the former turned his marker well on six minutes to thump in a daisycutter that flew across Kelvin Davis but out for a goal kick.
But it was Varney that could and should have fired Wednesday in front moments later. McAllister sent over a teasing far post cross that landed perfectly for the Rams man six yards out but Varney shot high over the bar with the goal gaping.
Jeffers had a low shot deflected wide as the Owls continued their dominance, while Southampton seemed content to soak up the pressure and hit the hosts on the break.
And that tactic backfired badly on 25 minutes when Varney sent Wednesday into a deserved lead.
Jeffers picked up possession on the halfway line and caught a high Saints rearguard square by nudging through to Varney, who kept his cool to advance and slot calmly past Davis.
Southampton were stung into life and hit straight back with David McGoldrick sending a clear header high over the bar. The same player was then denied by a brave Tommy Spurr block on the edge of the six-yard box after good work from Bradley Wright-Phillips down the left flank.
But Saints almost found themselves two goals down on the half-hour mark when Etienne Esajas delivered a delightful feed right into the path of the leaping Varney, who glanced a close-range header wide with Davis rooted to his line.
The Owls should have paid for that profligacy five minutes before the break as Jason Euell was presented with a gilt-edged opportunity to equalise.
Rudi Skacel escaped the attention of Lewis Buxton and squared accurately for Euell, whose sidefooted effort from 12 yards was goalbound until Lee Grant intervened with a top-drawer save low to his right.
Jeffers took a knock just before the half time whistle and failed to emerge for the second period, handing Jermaine Johnson a chance to impress.
But it was Southampton that started with greater urgency after the resumption and the south coasters were almost rewarded on 54 minutes. Euell held the ball up well a yard inside the Wednesday penalty area and nicely teed up the advancing McGoldrick, whose rising shot just evaded Grant's upright.
The visitors desperately needed something from the game and had little to lose by pouring men forward. Boss Mark Wotte also introduced striker Marek Saganowski from the bench to add more firepower in the final third.
But the Owls came close to thwarting those plans with Esajas only denied by a brave last-ditch tackle by Lloyd James following Varney's intelligent feed across the danger zone.
And they positively destroyed them on 72 minutes when Varney took advantage of some slack Saints defending to double his and Wednesday's tally.
The on-song striker pounced on a loose ball midway in the Southampton half and skipped past the advancing Davis to tap home into an empty net.
That second strike knocked the stuffing from the visitors, who gamely battled on but failed to penetrate a comfortable Owls rearguard and went down the tunnel staring right in the face of relegation.
Owls: Grant, Buxton, Wood, Hinds, Spurr, Tudgay, McAllister, Potter, Esajas (O'Connor 89), Jeffers (Johnson 46), Varney
Unused substitutes: Simek, Beevers, Boden
Southampton: Davis, Perry, Saeijs, Skacel (Saganowski 63), Wotton, Surman, Lallana (Smith 71), James, Euell, McGoldrick, Wright-Phillips (Schneiderlin 82)
Unused substitutes: Forecast, Liplak












