The SpaceX CEO on Tuesday wished Blue Origin's crew, including founder Jeff Bezos, good luck on Twitter ahead of the company's first crewed spaceflight – the 52nd anniversary of the Apollo 11 moon landing.
"Best of luck tomorrow!" Musk replied to a Blue Origin Twitter post showing the mission's passengers.
Bezos will become the second billionaire to ride his own rocket, following Virgin Galactic founder Richard Branson's lead earlier this month.
Musk has publicly supported both Bezos and Branson's efforts – despite the fact that his company is also racing to take tourists into orbit.
On July 11, Musk visited the Branson – who has insisted this isn't a space race – before his historic flight with five crewmates over the New Mexico desert.
"Great to start the morning with a good friend," Branson wrote.
Earlier this month, Musk also defended the space race between some of the world’s richest men, saying space "represents hope for so many people."
SpaceX, which is already launching astronauts to the space station for NASA and building moon and Mars ships, is planning to have the company's first private flight in September.
The Associated Press contributed to this report.