The Chelsea caretaker, having seen his last chance of winning silverware this season disappear at Goodison, conceded that Costa’s lack of fitness contributed to his frustration that mounted as Everton, led by Gareth Barry, clearly used the full extent of the law to try and rile the combustible striker.
It worked, in the 84th minute, when Costa, cautioned early for a retaliatory foul on Barry, squared up to the midfielder again, placed his head on his rival’s and appeared to think about biting him before realising the gross error in his judgement.
Luis Suarez this was not but, still, the FA will feel obliged to look at the incident, via referee Michael Oliver’s report, and while the backlash against the Chelsea man will not be as furious as that against the former Liverpool player, Costa is clearly the Premier League’s reigning enfant terrible.
“When I did not know Diego from the inside, which I now do since December, you have to get used to each other,” said Hiddink.
“I have sympathy for him but nevertheless also talk about how he can control himself. He did halfway through the season and after that he was different in his behaviour. I do not have any guarantee – because he is not a machine he is a human being – that he will not one time explode a bit.
“I have not seen him go over the edge since December. This is now maybe the first time in his frustration at not being totally fit – but again I will have to see it. It’s a relation of frustration and you act, and if the opponent knows you are vulnerable, there is big theatre.
“The opponent can be professional and say I will give him a bit and he is reacting.”
It appears likely the FA will take no action with Barry’s own words defending Costa, over the bite allegation at least, and Hiddink hopes that there will be no mass reaction against his player, as there was when Suarez received a 10-man suspension for biting Chelsea’s own Branislav Ivanovic three years ago.
Costa had insisted on playing at Goodison even though an injury he sustained in the midweek Champions League exit to PSG should have seen him rested.
That fact, coupled with Chelsea’s second cup exit in a matter of days, clearly did not help the striker’s mood, or his ability to control himself.
“That’s true,” said Hiddink. “That gives him frustration because he eagerly wants to play, wants to play. You see medically we should have said Champion League is difficult and FA Cup today is difficult because of the presence of little injuries.”
“But he was desperate and he made a difference against Paris. In principle I protect every man but it’s not good to do something stupid.”
The pity, for Everton and Romelu Lukaku at least, was that Costa’s late implosion - added to three minutes from time when Barry deservedly also received a second yellow card for a foul on Cesc Fabregas - detracted from two sensational goals by the Belgian and a victory that eased pressure on manager Roberto Martinez.
New Everton co-owner Farhad Moshiri attended his first game since buying a 49.9% stake and spoke of his desire to keep key assets at the club although Martinez conceded that should Chelsea make a ludicrous bid to buy back their striker, his club might not be able to resist.
“I said many times Cristiano Ronaldo was sold by Manchester United so if Manchester United cannot keep Cristiano Ronaldo that is a sign of a modern game,” said Martinez.
“If you sell a player for those sort of amounts I think you can get the benefit of adding three or four players.
“We have got big projects and Mr Moshiri mentioned that we are going to sit down in the summer and make a decision with what the next step is with Goodison - a new ground or developing Goodison - we want to be a Champions League club, have a winning team.
“That is what every Evertonian wants to do.”
Robles 7; Coleman 7, Jagielka 6, Funes Mori 5, Baines 6; McCarthy 7, Barry 6; Lennon 8 (Stones 88), Barkley 7 (Besic 90), Cleverley 7; Lukaku 10 (Niasse 90). Subs (not used) Kone, Deulofeu, Osman, Howard.
Courtois 6; Azpilicueta 6, Cahill 5, Ivanovic 5, Kenedy 5 (Terry 85); Mikel 7, Matic 6 (Remy 82); Willian 6 (Oscar 73, 6), Fabregas 6, Pedro 5; Costa 5. Subs (not used) Begovic, Baba, Traore, Loftus-Cheek.
M Oliver 6