Traditionally a rocket would launch into space, drop off its payload, and then be lost forever. But the return landings of rockets could dramatically cut costs of space missions.
But rival Jeff Bezos, the chief executive of Amazon and founder of his own space startup Blue Origin, was quick to point out that Musk wasn't first to achieve the feat in what was a backhanded compliment.
Last month, Blue Origin carried out a similar return rocket landing test. The difference however is that Bezos' attempt was carried out during a trial while SpaceX nailed the landing during a real mission. Also, Blue Origin' rocket was on a "suborbital" flight so didn't go as high as the Falcon 9.
While Bezos has fired shots at Musk this time around, it was the Tesla boss who originally kicked things off, pointing out the difference between "orbital" and "suborbital" flights.
Bezos had not responded to Musk at the time of publication.