There was to be no great escape for Middlesbrough as a home draw with Aston Villa all but condemned Gareth Southgate's side to the drop.
Southgate was booed off the Riverside pitch at the end of a tense affair where Boro gave everything but once more fell short.
Tuncay's glittering overhead strike combined with results elsewhere in the relegation battlefield had given Middlesbrough some hope.
But, in a 90 minutes that summed up their season, a failure to finish off a sluggish Villa side led to nervousness, panic and then the inevitable equaliser by John Carew.
Boro's predicament means they must now win their remaining fixture at West Ham - and hope Newcastle lose at Villa and Hull concede a hatful at home to champions Manchester United.
Stranger things have happened but a decade of Premier League football at the Riverside now looks at an end.
The fraying Premier League lifeline had unravelled for Boro even before kick-off after Jeremie Aliadiere failed to make the squad due to an ankle injury.
Yet Middlesbrough's urgency was evident from the opening seconds when Stewart Downing nearly contrived a goal, bursting into the box and cutting the ball back towards three red shirts but Gareth Barry's unflustered interception saved the visitors.
Tuncay flashed a header over the bar before Villa showed some quality with a neat build-up leading to Gabriel Agbonlahor trying to slide the ball under Brad Jones, who saved with his legs.
Middlesbrough could not afford to go behind and the sense of relief and hope when Tuncay opened the scoring with an extravagant strike resonated through the stadium.
Julio Arca played in Downing whose shot was deflected upwards for Middlesbrough's player of the season, with his back to goal, to produce an overhead kick that left Brad Friedel grasping thin air.
But a serious blow soon followed for Boro when Downing was left in agony after Stiliyan Petrov stood on his foot as the winger was in mid-flight. The England international left the pitch on a stretcher to a standing ovation having perhaps played his last game for his home-town club.
Marlon King came on for Downing and Tuncay dropped back into a deeper role in midfield, but the change did not appear to affect Boro while Villa continued to struggle to find their rhythm.
Justin Hoyte had a decent effort from 18 yards deflected over by Carlos Cuellar's head, then a couple of minutes later had another strike turned aside by Friedel after excellent trickery by 20-year-old Dutch striker Marvin Emnes.
Tuncay delivered another power overhead kick - but this time to clear the danger as Villa made a rare foray into the Boro box and the visitors' performance was summed up when Emile Heskey raced on to Petrov's pass and sliced his cross-shot hopelessly wide.
As news started to filter through from games involving Hull and Newcastle, the home crowd started singing the theme from 'The Great Escape', but it seemed too early to tempt fate.
Sure enough, the tension started to get to Middlesbrough and they wasted several chances to clear their lines as Villa pressed, though when King sliced a clearance to Carew's feet there still seemed enough bodies around the Norwegian to thwart him.
Panic ensured instead and Carew kept his calm to place an accurate shot through the gaps in the crowded goalmouth and into the net.
The goal was a dagger in the heart for Boro and Ashley Young nearly drove the blade deeper but shot straight at Jones.
Young should have finished it again when Robert Huth's misjudgment let in the Villa winger but Jones once more came to the rescue.
There were only half-chances for Boro after that, as talisman Tuncay sent a dipping volley over and then Tuncay landed a header on the roof of the net.
The players were cheered off at the final whistle but there were boos for Southgate who cut a sorry figure as he trudged off the turf.
Teams
Middlesbrough Jones, Bates, Wheater, Huth, Hoyte,O'Neil (Walker 72), Adam Johnson, Arca, Downing (King 23),Sanli, Emnes.
Subs Not Used: Turnbull, Taylor, Shawky, McMahon, Grounds.
Goals: Sanli 14.
Aston Villa Friedel, Milner, Davies, Cuellar, Shorey,Ashley Young (Reo-Coker 70), Petrov, Barry, Agbonlahor, Carew,Heskey.
Subs Not Used: Guzan, Sidwell, Delfouneso, Knight, Gardner,
Clark.
Booked: Milner, Barry.
Goals: Carew 57.
Att: 27,261
Ref: Mike Riley (Yorkshire).
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