Matheus Nunes' failure to deal with a low cross into the Manchester City box saw Brighton score the only goal on Saturday.
Maresca has have suffered back-to-back Premier League defeats for the first time as City manager as Yasin Ayari scored the only goal at the Etihad Stadium on Saturday in the 11th minute to give Fabian Hürzeler's side their first ever win at the Etihad Stadium.
Matheus Nunes failed to deal with a dangerous cross across the Manchester City box and the Seagulls took full advantage as the hosts were once again architects of their downfall, having given away a plethora of cheap goals in the last month.
The defeat was Manchester City 's third in their last six games in all competitions, following the 4-2 home loss to Paris Saint-Germain in the Champions League on 14 October and the 2-1 defeat at Aston Villa eight days ago.
Brighton moved to within two points of the Blues with the victory, three days after Maresca's side had needed a penalty shootout to knock the Seagulls out of the Carabao Cup at the Etihad Stadium.
Speaking to BBC Sport after the game, Maresca was asked about the number of goals his side have conceded recently. "I'm always concerned, even if we win games, for sure. We need to analyse the goals that we concede, and we need to improve that," the Italian said.
Maresca was then asked in his press conference about individual errors costing Manchester City in recent weeks. "Sometimes it happens. Unfortunately it's happening to our players, but I think it's part of the game, part of football - sometimes it happens," the City manager added.
"Probably in the last two, three games it's happened many times to us and we need just to analyse, understand what we can do better, and try to move on."
On the balance between the goals his side are scoring and conceding, Maresca said: "In this moment, I think we are second in terms of goals scored in the Premier League.
"That means we are scoring goals. Again, in this moment, probably we are conceding silly goals that we can avoid, and hopefully we can avoid in the next game."
Ayari's winner came after Matheus Nunes failed to deal with a low cross into the penalty area, with the Portugal international's attempted clearance falling for the Brighton midfielder to steer the ball past Gianluigi Donnarumma.
Nunes was passed fit by Maresca on Friday after missing the cup tie, and Donnarumma also played a loose pass into his own backline after the opener that was cleared before Brighton could double their lead.
At Villa Park last weekend, a loose touch from Marc Guehi inside the opening six minutes allowed Nicolas Jackson to score, with Maresca later backing the defender after he was withdrawn at half-time in Birmingham.
Jackson's winner around the hour mark then slipped beneath Donnarumma, who had also faced criticism after the defeat to Paris Saint-Germain, before Maresca insisted that no player is undroppable ahead of the Brighton rematch.
Geronimo Rulli started in goal for the Carabao Cup tie on Wednesday after Donnarumma was among five players given three days off , and the Argentine saved two penalties in the shootout before the Italy international returned on Saturday.
Their last two league defeats have ended a seven-match winning start under Maresca and allowed Arsenal to go three points clear at the top of the Premier League after their 1-0 win away at Liverpool on Sunday - with Brighton also now within two points of Manchester City .
Brighton goalkeeper Bart Verbruggen made seven saves at the Etihad Stadium, denying Iliman Ndiaye and Abdukodir Khusanov, whilst Nico O'Reilly headed a rebound against the post and Jeremy Doku was kept out in stoppage time.
City travel to Germany to face RB Leipzig in the UEFA Champions League on Wednesday - before visiting Nottingham Forest at the City Ground in the Premier League on Saturday ahead of the international break.
