LONDON - South Korea's Ki Sung-Yueng stunned Chelsea as the Sunderland midfielder's first goal for the club sealed a shock 2-1 win in the League Cup quarter-finals, while Manchester City swept into the last four with a 3-1 victory at Leicester on Tuesday.
Gus Poyet's team had been on the verge of defeat at the Stadium of Light after goal-line technology was used for the first time in the League Cup to give Chelsea the lead through Lee Cattermole's own goal in the opening minute of the second half.
But Fabio Borini equalised for the Premier League's bottom club in the 88th minute and Ki sent Sunderland into the semi-finals with a cool finish two minutes from the end of extra-time.
It was Ki's first goal in 13 appearances for the Black Cats since his loan switch from Swansea, with whom he won the League Cup last season, in September.
Ki had never scored in English football since moving to Swansea from Celtic in 2012, and this was his first club goal since he netted for the Scottish giants at Hibernian in February 2012.
It was a dispiriting night for Blues boss Jose Mourinho, who won the League Cup twice in his first spell in charge of the west London club but saw his fears about his shot-shy team confirmed during a lacklustre display.
Mourinho made eight changes following Saturday's 2-1 win over Crystal Palace and, after struggling to find any rhythm in a tepid opening 45 minutes, Chelsea took the lead less than 60 seconds after the break.
Frank Lampard was challenged by Cattermole near the goal-line as the pair competed for Cesar Azpilicueta's low cross and the ball rolled into the net.
Sunderland goalkeeper Vito Mannone tried to claw the ball out from behind the line, but the goal was correctly given, with referee Anthony Taylor pointing to his watch to indicate goal-line technology had been used to confirm the decision.