The Blues spent much of the game on the attack, and by halftime they had had 12 shots on goal. Only two of those shots were on target, and they were made to pay for their wastefulness when Swansea's bargain striker, Michu, capitalised on a Branislav Ivanovic error to send the visitors 1-0 up after 45 minutes.
It was more of the same in the second half as Chelsea pressed for the equaliser, but they were denied time and again by an excellent Gerhard Tremmel in the Swansea goal. The killer blow came in injury time, when another mistake by Ivanovic saw Danny Graham skip past Ross Turnbull to make it 2-0 before substitute Demba Ba put the ball in the net, only to be ruled offside.
This result gives Chelsea a huge task in the second leg at the Liberty Stadium if they want to reach their second cup final of the season.
Here are my player ratings for the Chelsea team. I start each player on 5/10 and points are awarded or deducted for positive and negative contributions.