Ki Sung-Yueng Sunderland
Sunderland midfielder Ki Sung-Yueng celebrates after scoring the winner against Chelsea in the Capital One Cup quarterfinals, December 17. Reuters

Ki Sung-Yueng gave Sunderland something to cheer about, scoring the winner against Chelsea in extra time to propel his side to the semifinals of the Capital One Cup, while Manchester City eased past Leciester to also book their place in the last-four.

The Blues will have one trophy less to worry about, after going down 2-1 in extra time to Sunderland, who will now look towards getting out of the desperate mires of relegation with a little more positive feeling.

"It's a competition that looks like it is not important -- it's cold, the stadium is not full, you play far from home," Chelsea manager Jose Mourinho said. "But, when you reach the final, you feel it as a nice competition you want to win.

"The players got the message because their attitude and ambition was good and they tried to play. They knew that I would go to the end of the competition with the players that had played more, like Mark Schwarzer and Kevin De Bruyne, so it's a pity that players like them can't play in the semifinals and the finals. I feel sorry for these guys."

After a goalless first half, Chelsea took the lead via an own goal from Lee Cattermole, who bundled-in a right-wing cross from Cesar Azpilicueta while under pressure from Frank Lampard, one of eight changes made by Mourinho on the day.

Chelsea were just two minutes away from sealing their passage through to the semis, only for Fabio Borini to come off the bench and force the tie at the Stadium of Light into the extra period.

Both sides had decent chances in the final 30 minutes, but it was Sunderland that made them count - Ki smashing the ball into the bottom corner past Schwarzer after taking a pass from Borini in the 118th minute.

"Everyone was desperate to win the game," Ki told Sunderland's official website. "The cup competition gave us a great chance to reorganise ourselves.

"The boys were really focussed on the game and from coming off the bench all I wanted to do was help the team go through to the next round."

At the King Power Stadium, it was business as usual for Manchester City, who powered into the final-four with a 3-1 victory over Championship side Leicester.

Aleksandar Kolarov opened the scoring for the away team in the eighth minute, with Edin Dzeko then putting City 3-0 ahead with a goal each either side of halftime.

Lloyd Dyer pulled one back for Leicester 13 minutes from time, but all it turned out to be was a consolation against the in-form English Premier League side.

"It was a very professional win, because it is not easy in one week to play Bayern Munich, Arsenal and then finish here playing in the Capital One Cup away," City manager Manuel Pellegrini said.

"It's normal that for Leicester they were very motivated for the game and so it was difficult to play this team at their home stadium.

"I think that the team played a very serious game and it is important to continue in this cup."