Tesla became the largest U.S. auto maker by market value on Monday, overtaking General Motors -- a feat that would have seemed highly improbable 13 years ago when the electric-car maker first began tinkering with the idea of making a sports car. From a report: Tesla climbed as much as 3.4 percent in early Monday trading, boosting its market capitalization to about $51 billion. The company was valued at about $1.7 billion more than GM as of 9:35 a.m. in New York. The turnabout shows the extent to which investors have bought into Musk's vision that electric vehicles will eventually rule the road. While GM has beat Tesla to market with a plug-in Chevrolet Bolt with a price and range similar to what Musk has promised for his Model 3 sedan coming later this year, the more than century-old company has failed to match the enthusiasm drummed up by its much smaller and rarely profitable U.S. peer. No matter, say investors who like the stock. Tesla is a technology player with the ability to dominate a market for electric cars and energy storage. To those same investors, GM and Ford are headed for a slowdown in car sales that will erode profits. "Is it fair? No, it isn't fair," Maryann Keller, an auto-industry consultant in Stamford, Connecticut, said of GM ceding the market-cap crown. "Even if Tesla turns a profit, they will eventually have to make enough to justify this valuation."