The Antichrist will take the place of God in many individual's hearts. That, however, does not describe the faith in/on Christ, nor does it describe what the opposite of faith in/on Christ represents.
When someone says they believe in a certain politician, it is understood that that individual believes in what that particular politician is preaching, and not that the politician is a politician, which is obvious.
Likewise, though the devils in Hell are quite aware of who Jesus Christ was and is, and thereby believed Him the son of God, they nevertheless do not believe in what Jesus preached. And what was it that Jesus preached? He preached to love God, who is love, and to love our neighbors as ourselves; to believe in truth, and justice, and all other spiritual qualities that are contrary to the flesh.
The Samaritan in Luke 10 regarded as a gentile, and who never heard of Christ, believed in loving his neighbor, and thus believed in Christ. The priest and the Rabbi on the other hand, who supposedly believed in God; their not believing in loving their neighbor, in their non-deed showed that they truly did not believe in God, who is love.
If then to love my neighbor and cling to spiritual qualities is to have faith in Christ, then to hate my neighbor and cling to fleshly lusts is to not have faith/belief in the Spirit, which is Antichrist.
When 1 John 2:22 describes Antichrist as individuals who deny both Christ and God, what is described are people who deny the teachings of loving our neighbor as the Way in which people should conduct themselves, and instead choose to follow after other Christs (where Christs represent politicians who claim to know the way, but whose proclamations deny God/love as the Way).
1 John 2:22 Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son.