The Swans booked a place in the Capital One Cup semi-final for the first time in the club's history after a narrow 1-0 win over Middlesbrough at the Liberty.
It took a Seb Hines own goal after 80 minutes to settle the tie, which proved a game of few chances.
The defender misdirected his header into his own net after Jonathan de Guzman curled in a corner.
The closest the Swans had gone before that was via a de Guzman free-kick, which was tipped onto the crossbar following a fine fingertip save from keeper Jason Steele.
It was far from a classic, but it was enough to ensure the Swans were in the hat for the semi-final draw next Wednesday alongside League Two club Bradford, Aston Villa and either Chelsea or Leeds.
The Swans made four changes to the starting line-up.
Michael Laudrup handed starts to Dwight Tiendalli, Garry Monk, Leon Britton and Itay Shechter as the suspended Ashley Williams sat this one out while Angel Rangel, Ki Sung-Yueng and Danny Graham among the substitutes.
The visitors included former Swans loanee Marvin Emnes on the bench, while another ex-Swan loanee Josh McEachran was unavailable as parent club Chelsea didn't want him cup-tied.
Swans: Gerhard Tremmel, Dwight Tiendalli, Garry Monk (capt), Chico Flores, Ben Davies, Leon Britton, Jonathan de Guzman, Michu, Nathan Dyer, Wayne Routledge (Ki Sung-Yueng, 65), Itay Shechter (Luke Moore, 55).
Subs: David Cornell, Angel Rangel, Kyle Bartley, Kemy Agustien, Danny Graham.
Middlesbrough: Jason Steele, Justin Hoyte, Andre Bikey (Andrew Halliday, 64), George Friend, Grant Leadbitter (capt, Ishmael Miller, 81)), Nicky Bailey, Emmanuel Ledesma, Seb Hines, Lukas Jutkiewicz, Scott McDonald, Faris Haroun (Richard Smallwood, 65).
Subs: Jayson Leutweiler, Kevin Thomson, Marvin Emnes, Stuart Parnaby.
The Swans saw early efforts by Michu and Nathan Dyer blocked before the visitors replied with Lukas Jutkiewicz heading straight at Gerhard Tremmel as the game started slowly.
Middlesbrough then created the best chance of the game so far, George Friend bursting down the left flank before cutting back to skipper Grant Leadbitter, but his low show was saved by the stretching Gerhard Tremmel.
It took a while for either side to really threaten, with Itay Shechter's header from Ben Davies' cross deflecting off Nathan Dyer but keeper Jason Steele gathered.
Then Boro went close again, Faris Haroun finding Leadbetter inside the box, but the captain's effort was punched out by Tremmel.
Dyer's deflected shot failed to Steele before Ben Davies' fine run set up Michu, but his shot was blocked out for a corner by Andre Bikey in the last action of the first half.
Half-time: Swans 0 Middlesbrough 0
Boro captain Leadbitter was the first to threaten in the second half, with his dipping shot collected by Tremmel.
Michael Laudrup made his first change after 55 minutes as Luke Moore replaced Itay Shechter.
Moore made an impression straight away, as he latched onto Wayne Routledge's header, but the striker appeared to be pulled down by Andre Bikey although referee Lee Probert waved away the appeals.
Laudrup made another change, Ki Sung-Yueng replacing Routledge just after the hour as the Swans went in search of a winner.
Ki immediately set up Jonathan de Guzman, but the midfielder's low shot failed to trouble Steele.
The Dutchman then went within inches of opening the scoring, his 20-yard free-kick looked destined for the net before Steele tipped it onto the crossbar and then Michu was penalised for a foul in his pursuit for the loose ball.
The Swans then saw a penalty appeal turned down as de Guzman's fine ball found Ki, and when Seb Hines dived in, the South Korean hit the deck. But Probert again rejected the appeals.
Michu then saw his shot blocked after a through ball from Ki as the Swans upped the pressure going into the last ten minutes.
And the pressure told in the 80th minute, de Duzman curling in a corner and Hines mis-directed his header into his own net.
Hines went close to levelling with two minutes left as he met a corner just two yards out, but the defender's header flew high over the crossbar.
Five minutes of added on time was to follow, with Moore going close after being teed up by Michu.
But the Swans held on to book their spot in the semi-finals.