Middlesbrough's defensive "naivety" cost them in Wednesday's 4-2 Premier League defeat by Hull City, says head coach Steve Agnew.
The Teessiders ended up shipping four goals to their relegation rivals at the KCOM Stadium and now sit in 19th position - seven points off the final position of safety.
Maguire's diagonal ball was crossed first time by Grosicki from the right and with Valdes stranded, Hernandez steered home his fourth league goal of the season.
The Tigers produced arguably their bets performance of the season to move out of the bottom three thanks to goals from Lazar Markovic, Oumar Niasse, Abel Hernandez and Harry Maguire.
The game started at a breathtaking pace, typical with both sides in relegation trouble, and it was Middlesbrough who drew first blood when Negredo slid home Adama Traore's cross in the fifth minute. To score the goal early on, from that goal we got carried away with the emotions of the game.
Hernandez followed that nuisance value by creating Hull's second, the Uruguayan capitalising on Ben Gibson mis-reading the flight of the ball before passing to Niasse, who fired in from 12 yards.
Traore and Negredo combined again as Boro swarmed back on to the offensive and the latter's shot on the turn was kept out by Hull keeper Eldin Jakupovic before the home side swept into a 3-1 lead.
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But Boro refused to surrender. "The players remarked on the noise they made in the far corner".
Rudy Gestede's header from Stewart Downing's cross forced Jakupovic into a brilliant reflex save and Negredo curled a left-footed effort a whisker wide.
Middlesbrough reduced the deficit in first-half stoppage time in controversial circumstances.
There was initial confusion over whether the goal had been given as referee Michael Oliver went to consult with the linesman.
The second half began in the same frenetic style.
By the time the music had stopped shortly before 9.40pm, Hull had three precious points and Boro were a step closer to a Championship return.
Hull, though, emerged from the break and stuck to their task, deservedly restoring their two goal cushion with 20 minutes remaining as an unmarked Harry Maguire headed home Andrew Robertson's cross.