In this paper, we propose a new method for constructing $1$-perfect mixed codes in the Cartesian product $\mathbb{F}_{n} \times \mathbb{F}_{q}^n$, where $\mathbb{F}_{n}$ and $\mathbb{F}_{q}$ are finite fields of orders $n = q^m$ and $q$. We consider generalized Reed-Muller codes of length $n = q^m$ and order $(q - 1)m - 2$. Codes whose parameters are the same as the parameters of generalized Reed-Muller codes are called Reed-Muller-like codes. The construction we propose is based on partitions of distance-2 MDS codes into Reed-Muller-like codes of order $(q - 1)m - 2$. We construct a set of $q^{q^{cn}}$ nonequivalent 1-perfect mixed codes in the Cartesian product $\mathbb{F}_{n} \times \mathbb{F}_{q}^{n}$, where the constant $c$ satisfies $c < 1$, $n = q^m$ and $m$ is a sufficiently large positive integer. We also prove that each $1$-perfect mixed code in the Cartesian product $\mathbb{F}_{n} \times \mathbb{F}_{q}^n$ corresponds to a certain partition of a distance-2 MDS code into Reed-Muller-like codes of order $(q - 1)m - 2$.