There are several methods to cause a phase lag to make single-phase act like rotational polyphase ---- by using capacitors, inductive coils, iron cores, permanent magnets etc. It's beyond the scope of this forum.

Creating the phase lag (several methods used) was the real genius of Tesla. It is not as simple as OP presents it. Tesla's genius is glossed over.

A simple example ---- if you charge a capacitor through a coil (inductor) it does not happen instantly, there is a delay. You have created a lagged phase, which can give rotational direction.