It really depends on the context -- it is acceptable as informal speech in the US. It comes down to the socioelect you intend to learn. So perhaps "I already sa

It really depends on the context -- it is acceptable as informal speech in the US. It comes down to the socioelect you intend to learn. So perhaps "I already saw x" is not incorrect per se (from a Descriptivist point of view), but it sounds very colloquial and would not be found in formal writing.