Maresca's side were rocked by Liam Delap's early penalty and a second-half goal from former Chelsea winger Omari Hutchinson.
Chelsea's second successive defeat after their Boxing Day loss against Fulham left them without a win in their last three matches.
The west Londoners had emerged as surprise title contenders after an eight-match winning run in all competitions.
But Maresca had insisted throughout that spell that Chelsea's inexperienced squad do not have what it takes to win the title in his first season after arriving from Leicester.
And the Italian's prediction looks spot on after a shock result in Suffolk that leaves Chelsea in fourth place, 10 points behind leaders Liverpool, who have a game in hand.
"We focus game by game. We are not focused on title race or those things," Maresca said.
"It was a strange game. We had many chances but we could do many things better, defend better in some moments.
"Now we've finished the first part of the season, no one expected us to be where we are. It's a long race."
Third-bottom Ipswich climb within one point of safety after winning for the second time in their last four matches.
Kieran McKenna's side have renewed belief they can avoid relegation back to the Championship thanks to their first top-flight home win in 22 years.
"Special night for the club. First home win in the Premier League at Portman Road for 22 years and to do it against Chelsea was fantastic," McKenna said.
"Everyone involved with Ipswich can enjoy a glass of sparkly stuff tomorrow night and think about some of the moments we've had over the last couple of years."
Delap domination
Ipswich took the fight to Chelsea right from the start as Delap bullied the visitors' defence in pugnacious fashion.
Delap raced onto Leif Davis' inch-perfect pass in the 12th minute and went to ground after the faintest of kicks by Chelsea goalkeeper Filip Jorgensen.
Referee John Brooks awarded the spot-kick and Delap drilled into the bottom corner for his seventh goal of the season.
Cole Palmer almost levelled immediately when his free-kick from 22 yards smacked against the post.
Palmer's superb left-footed cross was converted by Joao Felix midway through the first half but the Portugal striker's powerful finish was disallowed for offside after a lengthy VAR check.
Just before half-time, Palmer's superb 20-yard curler looked destined for the top corner after Felix's lay-off, only for Christian Walton to brilliantly parry onto the crossbar.
Felix's header was cleared off the line by Wes Burns early in the second half before Walton thwarted Noni Madueke's low effort.
Chelsea's profligacy came back to haunt them as Ipswich doubled their lead in the 53rd minute.
Axel Disasi carelessly passed straight to Delap on the halfway line and he ran at Levi Colwill before passing back to Hutchinson.
Intelligently working a yard of space, Hutchinson drilled into the bottom corner.
It was a special goal for Hutchinson against a club that released him twice from their youth team.
Chelsea were unable to muster a response as Ipswich inflicted a painful defeat with repercussions at both ends of the table.
