The 24-year-old South Korea international's first goal in English football dumped Chelsea out of the competition on a famous night at the Stadium of Light as the Black Cats made light of their relegation fears to keep alive their hopes of cup glory.
But as the fans eagerly anticipated the semi-final draw, Ki and his team-mates were already starting to focus on Saturday's home clash with Norwich and the quest for a league victory to kick-start a great escape.
Ki said: "Chelsea are one of the best teams in England. Even though this is the League Cup, we don't care because we will get a lot of confidence from that.
"I think definitely it can help our league form. The atmosphere is buzzing among the boys and we all believe.
"If we can beat Chelsea, we can beat other terms. But we have to get our focus back for Saturday."
Ki's decisive intervention came in the final minute of extra-time at the end of a gruelling encounter which saw the Black Cats come from behind to overhaul Jose Mourinho's men.
Having already seen veteran keeper Mark Schwarzer keep out his goal-bound header, the former Celtic midfielder kept his head to work his way into a shooting position and then drill the ball past the Australian and into the bottom corner to snatch a shock win.
It was the first time Ki, who is on loan at the Stadium of Light from Swansea, had found the net since heading south of the border in August last year, and it came after fellow substitute Fabio Borini had cancelled out Lee Cattermole's 46th-minute own goal with just two minutes of normal time remaining.
Ki said: "I can't express the feeling. It's my first goal in England, a quarter-final against Chelsea and scoring in the last minute - that's maybe a once-in-a-lifetime experience.
"It was great to celebrate and to get through to the semi-final. I had a chance a few minutes before with the header, but I thought I would get another chance.
"The boys were desperate to win. They had a lot of energy and we were fitter than Chelsea. We controlled the game in extra-time."
The win was just Sunderland's fourth in all competitions since Gus Poyet replaced Paolo Di Canio as manager in October, and their first in six outings in the wake of another remarkable result, the 1-0 league victory over Manchester City on November 10.
However, while Poyet and his players now have a two-legged semi-final to look forward in the new year, there is little doubt as to where the focus must lie in the meantime.
Despite Saturday's 0-0 draw at West Ham, the Black Cats remain bottom of the table and five points adrift of the 17th-placed Hammers.
While cup success can only help to build confidence, they desperately need to start their points total ticking over in earnest if they are to avoid the fate which has more often than not befallen the club sitting bottom of the Premier League table at Christmas.
They face home clashes with the Canaries and Aston Villa either side of trips to Everton and Cardiff around the turn of the year, and their efforts on their own pitch seem likely to be pivotal.
Poyet and his staff will spend the next few days trying to soothe tired legs and minds, but Ki is confident the euphoria of cup success will do part of the job for them.
He said: "If we had lost in extra-time, we would be disappointed because we had done well in the game. But now you don't feel it as much physically.
"I don't think we will be mentally or physically tired. We have three days to prepare before Norwich, which is enough time."
Chelsea boss Jose Mourinho will spent the weekend mulling over a frustrating night on Wearside as he prepares for Monday's crucial league trip to Arsenal, but insisting his team does not have a mental block over killing teams off.
He said: "I don't think it's a mental block because we played very well. With a mental block, you don't play. Every team with mental blocks, they don't want the ball.
"They feel comfortable without the ball, they feel comfortable defending and not having the responsibility to have the ball.
"This team is very far from a mental block because the team arrives at every stadium, gets the ball and plays and dominates and creates, so it's not a mental block, for sure. We don't have this problem."