Liverpool named Kelly in his team for the first time since September 23, 2012 - when the No.34 suffered an anterior cruciate ligament rupture in his right knee.
He told Liverpoolfc.com: "It was brilliant. I was probably more nervous for this match than any I've ever played for Liverpool, because after 15 months that was my first start.
"It was great to get that behind me, getting up and down the line. I was getting cramp in my calf about 65 minutes in, but it was brilliant for me to get 90 minutes.
"A good cup run, for me, is vital in terms of games. I've been getting them this season due to no Europa League. We can just keep going in the cup games and we're doing well in the Premier League.
"We did what was needed, we got through to the next round. It was a good, strong performance overall from the lads."