Notorious short-seller, Andrew Left of Citron Research.

Notorious short-seller Andrew Left has reversed direction and gone long on controversial electric vehicle company Tesla Inc. (TSLA - Get Report) . 

Tesla was riding high Tuesday, with shares up more than 9%%. Tesla is expected to report earnings after the closing bell on Wednesday, Oct. 24.

"Citron is long Tesla as the Model 3 is a proven hit and many of the TSLA warning signs have proven not to be significant," Left wrote in a note Tuesday, Oct. 23. Left sued Tesla in September for allegedly misleading investors over plans to take the company private.

Left's rationale for changing his opinion on Tesla? "Plain and simple -- Tesla is destroying the competition," he said. Electric vehicles are certainly becoming an important part of the future of transportation, and several Tesla competitors in the EV space have emerged, such as Chinese electric vehicle maker Nio Inc. (NIO) , which went public on the New York Stock Exchange last month. Volkswagen Group (VWAGY)  also has plans to launch an electric car soon.

While the Tesla Model 3 is selling well, Left said investors should recognize just how wide the margin is between Model S sales and sales of other EV brands. There have been 8,000 Model S deliveries in the third quarter, with the runner up, the Lexus LS, delivering 2,303 deliveries in the same time frame. 

"It looks like it is the competition that is taking the Ambien," Left said. 

Of course, the last ingredient to Left's go-long thesis is profitability. Tesla can sell all the cars it wants to, but it has to be profitable. Left is a believer.

"Tesla will, finally, after 10 years of unprofitable existence, have the ability to prove that it can be a sustainable, highly cash flow generative entity that is no longer reliant on the capital markets." Tesla has long been valued on its ability to raise debt, even while unprofitable, but $900 million of debt principal due in March 2019, a shrinking cash pile, and fears regarding competition among others on Wall Street have all caused the share price to plunge more than 8% this year.

But a strong quarter, Left thinks, could rid Tesla of the need to raise capital, reflecting the ability to sustain future profitability. "A strong quarter removes the overhang of a necessary capital raise -- we suspect that Tesla will be generating more than enough cash to both fund aggressive growth plans and build cash on the balance sheet," Left said.