But superb bowling from Ben Sanderson (4-63) and Jack White (4-62) saw the home side bowled out for 335, a lead of just 32.
Openers Ricardo Vasconcelos and Emilio Gay wiped out that deficit before falling in quick succession along with Rob Keogh, and thatleft the County in a bit of bother at 64 for three.
But Rickelton, who made a brilliant 101 not out, was joined by Jimmy Neesham (91) and the pair put on 158 for the fourth wicket to put John Sadler's team in a strong position going into the final day.
Northants closed on 284 for five, a lead of 252, with Rickelton and Lewis McManus (4no) at the crease.
“It was pretty tough when I walked in there to be honest, it was tough to score," said the South African, who also scored a century on his County debut against Warwickshire.
"The ball was stopping and they were getting some variable bounce so I was just trying to make sure that they weren’t going to get me out.
“Jimmy came in and took the pressure off me quite nicely and then allowed me to get into my innings.
"It set the game up nicely for hopefully a big finish."
And he added: "The partnership was crucial, obviously it took the game away from them.
"Jimmy came out with a bit more of a counter-attacking style, was willing to take risks for the reward and things worked out nicely for him.
"He was nine short of a hundred and I thought he really deserved it, but he’s put us in a good position now and we can hopefully dictate Thursday's session.”
Looking back on the spectacular morning session with the ball, Rickelton added: “The start was beautiful, I don’t think you could have scripted it any better for us to be honest.
"At five down we thought we were settling in until at least the afternoon session, but Jack and Sandy really put up their hand and made inroads which made our lives a lot easier.
"Any lead’s a good lead so it was nice to get over that and set it up for the final day."
Kent's Daniel Bell-Drummond admitted it was a tough day for his side, but called on the home side's bowlers to take what Northants did first up on day three as their inspiration.
“If we can try and do what they did to us, get five wickets before lunch and get chasing around 300 it would obviously be a very good game," he said
“We were pretty positive, but those things happen and we’ve just got to go and do it to them on the final day.
"They collapsed in their first innings so it’s potentially one of those wickets where if you keep the dots up and dry them up then wickets could potentially fall in a heap.
“Whatever the target is ultimately we respect them, they’re a very good team, they won’t make it easy for us and we’ve got to get the breakthrough in the morning to make the win a possibility.”
Play resumes at Canterbury at 11am.