Swansea are into the last four of the League Cup for the first time in their history but local celebrations were muted by the poverty of a low-grade quarter-final settled by an own-goal from Seb Hines after 81 mundane minutes.

The Welsh team's disjointed, feeble performance was horribly reminiscent of their first half against Norwich City last Saturday, after which they were 3-0 down. Middlesbrough were left feeling hard done by after creating most of the few goalscoring opportunities there were.

This is the farthest the Swans have been in a major knockout competition since they reached the semi-finals of the FA Cup in 1964 but their incoherence on Wednesday night was reflected in the fact that Michu, the Premier League's leading scorer, was denied a worthwhile chance. Starved of possession by an ineffective midfield, the much-coveted Spaniard was forced to drop deep in vain search of the ball. It was only after the introduction of Ki Sung-yueng midway through the second half that the tables turned. The Korean ran at the Boro defence with a penetrating directness that nobody had shown before his arrival.

Promotion is Middlesbrough's priority as Tony Mowbray confirmed before and after the match, but 600 of their fans had braved the discouraging journey. "After travelling six and a half hours to get here, they will have expected us to give it a real go, and we did that," said Tony Mowbray. "With a bit more luck we could have won. It's frustrating we didn't but we did OK away to a mid-table Premier League side and can take heart from that." Choruses of "Going up" throughout the tie reflected the visiting supporters' pronounced preference.

Ashley Williams, the Swans' captain, was suspended and gave way to Garry Monk in central defence and Angel Rangel was rested, with Dwight Tiendalli coming in at right-back. Boro were without Josh McEachran, the young midfielder on loan from Chelsea, the terms of his temporary transfer precluding involvement in the knockout competitions. Nick Bailey, his understudy, was a strong contender for man of the match honours after subduing Swansea's vaunted midfield. Jonathan Woodgate was injured, as is his wont, and replaced by Hines who, attempting to atone for the own-goal, headed the last chance of the match over the bar.

The football Mowbray's team play is as good as any in the Championship and they had much the better of the first half. Grant Leadbitter's early incursion into the penalty area was shut out by Chico Flores's timely intervention and, when the midfielder tried his luck again, from the 18-yard line, his shot was too close to Gerhard Tremmel, who needed all the reassuring touches he could get after his culpable performance against Norwich.

Swansea's first strike at goal was delayed until the 35th minute, when Itay Shechter met Ben Davies' left-wing cross with a glancing header which had Jason Steele flying to his left. Boro's response was instantaneous, the persistent Leadbitter warming Tremmel's hands on a night when all present were grateful for any heat they could find.

For the second time in five days the Liberty Stadium crowd were unimpressed by their team's first-half efforts, falling into a silence that was interrupted only by groans of disapproval.

During the interval Michael Laudrup told his charges to relax and play their football and simplicity was genius. Swansea improved in the second half sufficiently to start threatening Boro's goal at last. That said, their first strike of consequence was delayed until the 74th minute, when Jonathan de Guzman's 25-yard free-kick had Steele fully extended in touching the ball on to his crossbar.

Swansea thought they should have had a penalty four minutes later when Steele, rushing out to meet the danger, brought down Ki but also made contact with the ball with his trailing leg. The home crowd were still abusing Lee Probert for turning down the appeals when the stalemate was broken, De Guzman's corner from the left and Monk's challenge panicking Hines into heading the ball into his own net.

It was a fitting, scruffy conclusion to a tie of disappointingly poor quality. "It wasn't a brilliant game to watch, it was a tight cup tie," said Laudrup. "In the first half everybody wanted to win but wanted it too much. Sometimes, if you want something too badly, you can't produce what you're capable of. The players took too many touches and ran with the ball too much instead of passing it. In the second half they relaxed and played more one- and two-touch football. The game never reached a high level but everybody here can be proud that we are through to the semi-finals."