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 win over Premier League Aston Villa on Tuesday, Swansea's victory over their top flight rivals was still a surprise.
Both Swansea goals came as a result of two errors by Chelsea defender Branislav Ivanovic.
In-form striker Spanish striker Michu, signed for just £2 million ($1.23 million, 1.59 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, managed by Denmark great Michael Laudrup, 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.