Scott McDonald scored a first-half hat-trick as Middlesbrough hammered Hull to put a major dent in City's hopes of claiming a play-off place.
Jay Simpson's close-range shot put Hull ahead, but McDonald scored twice with two 12-yard strikes in quick succession to swing the game Boro's way.
Julio Arca added a third from close range before McDonald completed his treble on the stroke of half-time.
Anthony Gerrard's 30-yard strike pulled a goal back for Hull.
The result means Hull miss out on the chance to go level on points with sixth-placed Nottingham Forest and two other sides - Leeds and Burnley - who are chasing a spot in the play-offs.
The Tigers remain on 63 points, three points behind the aforementioned teams with three games to play.
Boro have spent the season languishing in the lower reaches of the table but they produced a first-half masterclass here to blow away their opponents and secure a victory that mathematically ensured they will be playing Championship football next season.
It began so well for the home side when Simpson latched on to a pass from Richard Garcia and drove a left-footed shot into the top corner from six yards out in only the third minute.
But before the quarter-hour mark, the home side found themselves trailing after McDonald struck two right-footed shots past home keeper Vito Mannone, both from close range.
Arca's strike in the 26th minute and McDonald's third goal, three minutes into first-half injury time, decided the game in the away side's favour.
With 21 minutes to go, Gerrard scored arguably the goal of the game when he lashed in from 30 yards, but by then it was never going to affect the result.