The County won the toss and inserted the visitors, but were perhaps made to rue the decision as Kent posted 286 for two in 96 overs, with the Ben Compton making 125 not out from 267 balls.
It was the in-form opening batsman’s fourth century of the summer so far, and his seventh score of more than 50.
Daniel Bell-Drummond made 83 and England man Zak Crawley 62, while for Northants there was a wicket apiece for Matt Kelly and Ben Sanderson.
Assistant coach Liddle, who is also the Northants bowling coach, admitted they had thought the pitch was going to be livelier than it has turned out to be, but said he couldn't fault the efforts of his bowlers.
“We felt there would be something in the wicket especially after the rain the night before and the cloudy overheads," said Liddle on the decision to bowl first.
"The stats say that not many teams have lost the game bowling first here, so we thought there was enough in our favour, but it turned out to be a bit flatter than expected.
“It is still a good cricket wicket; you have to bowl well to get wickets and bat well to get runs.
"I can’t knock the lads.
"They have run in and hammered the wicket and made it difficult for the batters to make scores. The lads keep standing up and putting performances in.
"Hopefully someone gets a few wickets and get a five-for otherwise it is a good team performance.
“There won’t be any change on Friday. We want to make it difficult for them and hopefully take some wickets as we go.”
Kent's Compton said: "A couple of us struggled to get good starts and we had to work hard as they bowled tight.
“I don’t get bored out there, I’m just trying to do a job for the team. I know I need to bat long and be the glue and get us a strong platform at the top.
“It was tricky and I struggled for rhythm until I got to about 50-something.
"I grafted but Deebz (Bell-Drummond) and I understood it wasn’t a pitch to feel a million dollars.
"It is a bit on the slow side so I had to work through it and it got better.”
Day two starts at the County Ground at 11am on Friday.