The 24-year-old scored the winner with 90 seconds left in extra time to complete a dramatic comeback after Fabio Borini had scored in the 88th minute to cancel out Lee Cattermole's own goal.
The South Korean international now hopes that the win will improve morale within the Black Cats' camp after their poor start to the Premier League season.
"I think definitely it can help our league form. The atmosphere is buzzing among the boys and we all believe," Ki told the Shields Gazette.
"Chelsea are one of the best teams in England. Even though this is the League Cup, we don't care, because we'll get a lot of confidence from that.
"I think 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.
"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.
"If we can beat Chelsea, we can beat other teams."
Ki's 118th-minute goal was his first since February 2012 when he scored for Celtic, with the on-loan Swansea player saying he was "desperate to get one".
"I was pushed forward. In the last game at West Ham, I had a lot of chances, but couldn't score, so I was desperate to get on," he admitted.
"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."