The tie finished 2-0 on aggregate after a goalless draw at the Liberty Stadium, with Swansea's surprise victory at Stamford Bridge a fortnight earlier proving the difference as Rafa Benitez's side failed to turn the tie around.
It was a game of little incident by way of goal mouth action, although Eden Hazard grabbed the headlines after he was sent off following a minor scuffle with a ball boy who refused to return the ball.
So what we did we learn from Swansea's qualification for the Capital One Cup?
James Hanson is swamped by his teammates after equalizing against Aston Villa in the second leg of the Capital One Cup semifinal
Chelsea may well have been favorites to lift the Capital One Cup this season, but following their defeat to Swansea City a new name will be etched onto the trophy come cup final day on Feb. 24.
Swansea's victory over the Blues means they—along with Bradford, who beat Aston Villa 4-2 on aggregate in their semifinal—have reached the final for the first time in their history.
In fact, it is Swansea's first-ever major cup final in their 100 years as a club. Coming in their centenary season means that victory against the Bantams will prove all the more special for the Jacks should they go on to lift the trophy.
It's a shame from Swansea City's perspective that reaching the League Cup Final for the first time in the club's history has been overshadowed by the antics of one of their ball boys.
With the game still goalless entering the final 10 minutes, Eden Hazard attempted to retrieve the ball, but a Swansea ball boy refused to give it back, forcing Chelsea's Belgian midfielder to toe-poke it from his grasp.
Hazard was sent off for his part in the debacle, while the ball boy received minor treatment from a member of the Swansea medical team.
The ball boy's main intention on the night appeared to be wasting time rather than the job he was there to do—as tweets he sent earlier that day suggested—but Hazard also must shoulder his share of the blame.
That said, it was a sorry incident that could have been easily avoided had the ball boy simply done his job. It was doubtful the Blues would force their way back into the tie so late on anyhow and had it not happened, the headlines would have been focused on something much more positive—Swansea's achievement in reaching the final.
As for the contact Hazard made, did it warrant the youngster to writhe around in so much pain? Watch the video to see for yourself.
It's doubtful Chelsea fans will witness scenes such as their 2010 Premier League victory this season
With Manchester United already 11 points clear of Chelsea in the title race, the Blues' hopes of a fifth league crown look beyond them for this season.
What their defeat to Swansea City in the Capital One Cup semifinal also outlines is their inability to win matches that really matter this season.
This season the Blues could have already lifted three trophies in the Community Shield, Super Cup and Club World Cup. They lost in all three and were eliminated from the group stages of the Champions League.
It's a worrying trend.
With only the FA Cup to play for now, do they have what it takes to win it? Not on their previous showings, nor the second leg against Swansea where they failed to create much by way of goal-scoring opportunities on a night when they knew a minimum of three goals were needed to take them through.
That said, it's not a criticism of Chelsea to say they don't look like winning things this term. The team is very much in transition with an interim manager who is trying to steady the ship through some choppy waters following Roberto Di Matteo's dismissal in November.
The Blues have a talented squad of players and there's no doubt that regardless of what is achieved this season, they will be among the contenders for major honors again next season and beyond.
In devastating form earlier this season for Chelsea, it's evident that Oscar has suffered from a lack of game time since Rafa Benitez's appointment as interim manager in November.
The Brazilian has grown used to warming the substitutes' bench of late, with Benitez preferring Victor Moses in his system, and it has seen his form drop as a result.
Wednesday's draw with Swansea City saw the 21-year-old put in another lacklustre performance as he tries to rediscover his form. That will only come with games, though, and with Moses at the Africa Cup of Nations with Nigeria, he may get enough game time to find his touch.
But when his teammate returns, Oscar may have to get used to his previous role under Benitez.
It was a disappointing evening all round for Chelsea, with new signing Demba Ba no exception.
The Senegalese has become an instant hero at Stamford Bridge with three goals in his first six matches, but last night was his worst display by a distance.
He wasn't alone in that, with the Blues struggling to penetrate a disciplined and organized Swansea rearguard, but he will be disappointed he didn't impact the game as he has since his arrival at the club.
He was mainly working off scraps in his position as the lone striker, but the imposing Demba Ba we have seen score 16 times for Newcastle United and Chelsea this term wasn't there, proving after all that the new golden boy of Stamford Bridge can have an off day himself.
Regardless of what has gone on in the past with Rafa Benitez, it's now time Chelsea fans dropped their protests and got back to supporting the team.
Wednesday's poor performance was a mixture of key players underperforming, but also Swansea City putting in an excellent defensive display that contained the Blues and meant it was difficult for the likes of Juan Mata to have an impact.
But Chelsea's problems in this tie stemmed from the first leg at Stamford Bridge, where fans remain adamant they do not want Benitez in charge.
In the modern game, where supporters are often accused of being "plastic," it's admirable Chelsea fans are willing to stand by their principles, but anti-Benitez chants and the constant booing of his name has now gone a little too far. It has created a cauldron of pressure at Stamford Bridge that has evidently impacted on the team's home performances and added more pressure on the players.
We'll never know if this cup tie would have gone Chelsea's way if the situation was different, but for the sake of the remaining games in the season, Chelsea fans need to drop their protests. Benitez isn't going anywhere until the season is over, as per his contract with the club, and Blues fans need to accept it.
It's gone on too long.