Swansea produced the second surprise English League Cup semi-final first leg result in as many days after defeating Chelsea 2-0 at the European champions' Stamford Bridge ground on Wednesday.
If not as great an upset as fourth-tier Bradford City's 3-1 defeat of Premier League Aston Villa on Tuesday, Swansea's victory over their top flight rivals was still a surprise.
Both Swansea goals in a backs-to-the-wall effort came as a result of two errors by Chelsea defender Branislav Ivanovic.
In-form Spanish striker Michu, signed for just £2 million ($3.21 million, 2.45 million euros) from La Liga side Rayo Vallecano, scored his 16th goal of the season in the 39th minute with a curling shot from the edge of the box after Ivanovic miscontrolled the ball.
Chelsea boss Rafael Benitez brought Frank Lampard and Demba Ba off the bench in search of an equaliser but none came.
And in stoppage time, shortly after Ba had had a penalty appeal turned down on his home debut, Swansea's Danny Graham scored for the fourth match in a row after another Ivanovic mistake.
Now Welsh side Swansea will look to seal the tie in the second leg at the Liberty Stadium on January 23, with the prospect of an improbable final against Bradford in their sights.
"We've had some historic results already this season but to win here is very special," Swansea manager Michael Laudrup told Sky Sports.
"We had to defend a lot, they had a lot of possession but to be honest they only had three good chances all night," the Denmark great added.
"They gave us two goals but you have to score them. It was a marvellous fight, we are a team that always try to play but when you play the European champions away you have to change.
"There is still a mountain to climb, Chelsea have so much quality. We will have to play with the same intensity, they can still win and can score three or four goals against us."