Turkey international Tuncay broke the hearts of battling ten-man Stoke City by grabbing Middlesbrough's winner five minutes from time.
Promoted Stoke refused to give up the fight despite losing midfielder Amady Faye to a straight red card for a two-footed challenge on Mohamed Shawky ten minutes before the interval.
The Potters fell behind immediately when Boro's Brazilian record signing, Afonso Alves, rammed the free-kick into the top right-hand corner of the net.
Stoke then had to withstand heavy Boro pressure in the first 25 minutes of the second period and only avoided conceding a second goal when Stewart Downing blasted a 64th-minute penalty against the crossbar.
Seven minutes later Stoke gained reward for their grit when they drew level as the result of an own goal.
Liam Lawrence crossed from the right and Boro's new boy, Justin Hoyte, was put under heavy pressure from Dave Kitson as he tried to clear. But the ball hit Hoyte's thigh and then rebounded into the net off his arm.
While Stoke probably deserved their leveller it did not take Boro long to start pushing forward again and the visitors had to absorb heavy pressure in the final 20 minutes.
Boro might have regained the lead in the 76th minute but for a brilliant save by Thomas Sorensen as he kept out a solo effort from Alves.
Boro finally ended the Potters resistance in the 85th minute although Stoke felt there was an element of offside about the winning goal.
Substitute Didier Digard hammered a strong low cross into the box and Tuncay was standing completely unmarked, and looked offside, before turning and shooting strongly past Sorensen.
Stoke's protests were turned down and TV replays afterwards showed that the assistant referee had made the correct decision because Tuncay was played onside by Stoke substitute Andy Wilkinson.
Despite the defeat Stoke manager Tony Pulis can take plenty of positives from the performance because his side were by far the better team when they had 11 players on the pitch.
His opposite number, Gareth Southgate, will be relieved to have escaped with three points because his team rarely played the positive attacking football which they had shown in their earlier games.
Boro had a gem in Downing who constantly probed the Stoke defence and caused them ongoing problems with his crosses into the box.
Stoke did defend well in numbers with Leon Cort a tower of strength while Lawrence was quick to turn defence into attack with his strong breaks upfield.