“Is Vegas on the line?” Elon Musk asked on one of his nightly calls with his sales staff in September of 2018.

Las Vegas was. Cayle Hunter, just nine months into his job overseeing a Tesla Inc. sales team from an office not far from the Strip, waited eagerly for Mr. Musk’s next question.

“How many people did you sign up for pickup today?” asked Mr. Musk.

This was Mr. Hunter’s big moment: His team had scheduled 1,700 people to pick up their Model 3s in the coming days—a record—and he was proud to announce the achievement. The compact Model 3 was Mr. Musk’s bet-the-company shot at transforming Tesla into a mainstream auto maker and ushering in a new era of electric vehicles—and at that moment, Tesla needed to move thousands of them to stay afloat.

Mr. Hunter had set a record, but Mr. Musk wasn’t happy. The Tesla chief executive ordered Mr. Hunter to more than double the number the next day or else he’d personally take over.