Kilmarnock manager Alex Dyer vowed not to allow racist abuse from "one individual" to drive him out of his job.
Police are investigating after Dyer received a letter containing racist abuse on Monday.
The letter was delivered to Rugby Park after Killie suffered a fifth consecutive defeat and eighth loss in nine Scottish Premiership games when they went down to Livingston on Saturday.
Dyer answered his critic by guiding Killie to a 2-0 win at Motherwell on Wednesday night and then telling them that he would not be deterred.
Dyer said: "Someone sent me a letter that had racial remarks in it.
"I don't mind someone telling me that they want me to leave the football club because I'm not doing a good job. I can take that.
"But not to tell me about the colour of my skin, that someone else is better than me or better than my race. It's not right.
"It hurts but it's not Kilmarnock supporters, not Kilmarnock Football Club. They are not about that.
"They have been very good to me since I have been here. The owners, the supporters, the staff, the players, have been brilliant to me.
"It's just one individual that doesn't like the colour of my skin. It's as simple as that, and I can't do anything about that."
The former Charlton midfielder added: "I work hard every day, I give my all, because it's the job I love doing.
"I'm never going to let someone like that deter me from doing my job. Never ever.
"It's in the police's hands and they will get on with it now.
"The football club have been brilliant to me and I got a lot of support from a lot of people. A lot of letters and emails came through wishing me all the best."
While the pressure eased on Dyer, Motherwell boss Stephen Robinson is now feeling the heat after a ninth game without a win.
Well started brightly but Greg Kiltie netted four minutes before the break and the game was over in the 53rd minute after Danny Whitehall scored from the spot following Mark O'Hara's red card.
After losing the six points they gained as a result of Kilmarnock and St Mirren's Covid-19 breaches, temporarily at least until the appeals are heard, the Steelmen are now just two points off the bottom.
Robinson said: "We started the game well – as usual – and had chances that we didn't take when we were forcing all the play. They score with their first chance and our heads dropped.
"There was a lack of belief after that and our hands were tied after the penalty and the red card.
"We looked like we had no confidence and, if I'm being totally honest, we never looked like scoring a goal after that.
"Of course it's a worry when heads go down like that but that's what happens when you lose football matches.
"Ultimately, though, I've brought these players to the club and I've put them on the pitch. Some of them aren't performing and some have had their heads turned and possibly believe that they're better than they are.
"Unfortunately, that happens in football: you're at the mercy of agents and others but they're not playing at the top of their game, simple as that and I have to look in the mirror because it's my fault."
Motherwell suffered a blow when Trevor Carson went off injured on his home return from knee surgery but Robinson is hopeful it is not a major setback.
