Swansea celebrated reaching the semi-finals of the League Cup for the first time but it was with a limp rather than a strut against a gutsy Middlesbrough side.
For an hour, it was the Championship team who provided the touch of class until a crucial substitution and an own goal turned this quarter-final tie on its head.
Ki Sung-yueng stepped off the bench to spark Swansea into life as their opponents tired before an own goal nine minutes from time by Seb Hines took the Welsh club into the last four.
Michael Laudrup, the Swansea manager, said: "It's fantastic and a great achievement for the club. I am happy, relieved and proud we are in the semi-finals.
"But we want to go and take the next step into the final. It will be very special. Everybody thinks they have a possibility of getting to Wembley. It was a very tight cup game with not many great chances. It wasn't brilliant to watch.
"None of the players have played in a major final before and they wanted to win too much. When you are so close you get tense. We were too slow and had too many touches of the ball. Middlesbrough did well and put pressure on us.
"We weren't playing well and didn't reach a high level," Laudrup added, "but we were more relaxed in the second half."
Securing Premier League football for next season may well be the priority for both these clubs, but Tony Mowbray's Championship side, backed by 600 travelling fans transported by the tournament sponsors, have become well-adept at life on the road in this competition having been drawn away for the 12th tie in succession and wasted no time tearing into their hosts.
Captain Grant Leadbitter was denied in the opening minute by a Chico Flores' crucial intervention, though he had far more success disrupting Swansea's rhythm in midfield. Lukas Jutkiewicz and Nicky Bailey followed with efforts that forced saves from Gerhard Tremmel as Middlesbrough out-passed and frustrated their opponents.
Jutkiewicz and Faris Haroun bustled away to set up Leadbitter for the best chance of a scrappy half but Tremmel was again alert.
Swansea were lacklustre and their only chance of note in the first half was Nathan Dyer's deflected effort after they had finally got the ball wide and in space to Ben Davies.
Laudrup brought on Luke Moore and he immediately made his presence felt in a tussle with Andre Bikey. However it was the introduction Ki on 65 minutes that brought Swansea to life.
The South Korean international breached the gap between the midfield intricacy and their attackers, driving at Middlesbrough and putting the red shirts onto the back foot. That, in turn, released Dyer and when he was felled by Nicky Bailey, Jonathan de Guzman saw his curling free-kick athletically tipped onto the bar by Jason Steele.
However the tide has turned and suddenly Swansea besieged the visitors' area. Hines twice intervened to deny a goal, first escaping a penalty shout for his challenge on Ki and then as Michu was set to pull the trigger.
Yet by a cruel twist of fate, it was the centre-back who proved decisive, leaping under pressure from Gary Monk for De Guzman's corner, only to direct the ball into his own goal.
Mowbray said: "Cup competitions are decided on fine margins. It was a tight game and it's frustrating to lose.We could have easily won 1-0 rather than have lost 1-0.
"I thought Hines was magnificent all night, but that is the way football goes. He had a chance at the end and it would have been fitting had he scored.
"We came and gave it a go. It was a performance similar to what we have been producing. We went to the Stadium of Light and beat Sunderland and now we have come to another Premier League side, who are a mid-table team and given a decent account of ourselves."
Man of the match Ki Sung-Yeung.
Match rating 5/10.
Referee L Probert (Wiltshire).