The Reds cruised to a comprehensive Anfield victory courtesy of a Fernando Torres brace and strikes from Alberto Aquilani and Ryan Babel - and Kelly is confident the goal glut is a sign Rafael Benitez's side are ready to return to top form.
"We've showed it against Portsmouth that we have got good performances in us and there is a lot more to come," said the defender.
"It has been tough but you get that in football. We've pulled through it together and we've just kept working hard in training.
"It's getting towards the end of the season now but we just take it one game at a time. So we'll concentrate on the next one which is Lille on Thursday."
Kelly was introduced as a second-half substitute against Pompey to make his first Barclays Premier League appearance.
Having already figured in Europe for Liverpool this season, the 19-year-old is eager to continue his push for more first-team action.
"I've enjoyed it, it's been a long time coming," said Kelly. "I enjoyed it to come on and it was a special moment for me.
"I think if the manager gives you a chance, you've got to play as well as you can and you can't look out of place or the next thing you know your chance has gone. You've got to take your chances."