Hull's Sky Bet Championship play-off hopes were dealt a major setback as Jayden Fevrier's second-half goal earned Charlton a 2-1 victory at The Valley.
The Addicks, who led through Charlie Kelman's seventh goal of the campaign, ended a seven-game winless run and mathematically secured their safety.
John Egan had headed the Tigers level at the end of the first half but they have not picked up a victory in their last six matches, taking four points from a possible 18, as they failed to jump back above Wrexham and into the top six.
Hull were forced into an early change with Eliot Matazo, making his first appearance since suffering an anterior cruciate ligament injury in February 2025, going off in the 11th minute.
Charlton opened the scoring in the 20th minute through a sublime strike by Kelman. He raced on to Conor Coady's through ball, cut inside Semi Ajayi and found the top-right corner of the net from the edge of the penalty area.
The Addicks were good value for their lead after making a fast start.
Hull began to make some forward forays of their own in the closing stages of the first half but took until the fifth minute of seven additional minutes to really threaten Thomas Kaminski's goal. Top scorer Joe Gelhardt put his shot narrowly past a post from Liam Millar's cross.
It was a mistake by Harry Clarke which led to the Tigers equalising with seconds left of the first half.
The Ipswich loanee's misdirected header went out for a corner when the wing-back was under next to no pressure. Substitute Paddy McNair's deep delivery was nodded home from a tight angle by Egan - with goal-line technology notifying referee Tom Nield that the ball had gone over before it was hacked clear.
Fevrier produced an excellent cross which just evaded Harvey Knibbs while Gelhardt could only fire wide at the other end wide after Millar's shot was blocked.
Fevrier restored Charlton's lead in the 68th minute - the first time they have scored twice in a Championship match since January 31.
The on-loan Stockport forward produced a mazy dribble before sending a low left-footed finish past Ivor Pandur from 20 yards.
Kaminski held Mohamed Belloumi's shot as Hull, who have not won their final away league game for 19 successive seasons, tried to mount a response.
The Charlton keeper had a let-off after his poor punch dropped for McNair but the Irishman failed to get a proper connection on his volley.
Lyndon Dykes forced Pandur into a fingertip save as Hull started to leave gaps at the back.
Fevrier had a chance to add a third but the ball was cleared off the line in stoppage time.
Charlton's Nathan Jones:
"It's as good an achievement as I've ever had, but there is also a touch of disappointment. I think we should be higher than we are.
"We never do it easy. We have missed chances from five or six yards in all our home games and then we score two absolute bangers.
"The amount of pressure is immense. They were under pressure, because they want to get promoted. But the pressure of going down is totally different.
"We get individual clips of every team. If you looked at that in isolation then you'd never sleep because everyone has massive threats. We are evolving and haven't quite got there yet.
"It's real relief - it's not euphoria.
"If you asked me at the beginning of the season if I would have taken this, I probably wouldn't. But as the season has gone on, staying up is the first stage for us to move forward and do what we want to do, the first part is for us to be a Championship side.
"I'm proud of the group, the club and all my staff. What a day. This group finds a way to do enough when it is needed."
Hull's Sergej Jakirovic:
"For me it is unbelievable we cannot win one game in this part of the season. Every team in this league had those moments in their season, unfortunately we have that moment now.
"We have a very small chance (of reaching the play-offs) because if Wrexham take one point it is over. It is over but it still isn't mathematically over. You have hope but first we have to win our game. It is now a very big problem for us. Now it is not in our hands.
"We played much better in the second half than the first. In the first half we needed to be brave on the ball and take some risks.
"The goal is perfect but we can stop this, defend it better. We equalised from a corner, which was very good because we didn't show anything in the first half.
"Their second goal is unacceptable - the guy dribbles through three players. We tried everything but this is football - we missed our chances. Congratulations to Charlton."
