In a dramatic U-turn in view, the firm described Tesla as “destroyingt the competition” as the company “appears to be the only company that can actually produce and sell electric cars”.
The research note read: “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.
“Plain and simple – Tesla is destroying the competition.
“TSLA is not just pulling customers from BMW and Mercedes but also from Toyota and Honda.”
Shares in Tesla subsequently rocketed by nearly 6 percent to 277.86 at around 15:00 BST.
The change in heart from Citron Research today comes almost two years after the group first declared a “short” position in Tesla in March 2016.
Tesla stock would be slashed by 50 percent from its level of $180 a share at the time due to “supply and demand problems”, the long-term critics said.
Mr Left revealed he was suing Tesla last month and said today’s note “has no bearing on the current lawsuit”.
The Citron Research boss alleges that Telsa CEO Elon Musk fraudulently engineered his since-abandoned plan to take the carmaker private to “burn” short-sellers.
Mr Left’s lawyer said in a press release: “We believe Musk attempted to manipulate the price of Tesla securities with false and misleading tweets, in a directed effort to harm short-sellers.”
Last month saw Mr Musk settle a lawsuit from the US Securities and Exchange Commission (SEC), which resulted in Tesla and the CEO agreeing to pay $20 million each to the securities regulator.
Mr Musk had been accused of making “false and misleading statements” after tweeting he had the funding in place to take Tesla private at $420 (£322) per share.
The Tesla CEO first responded to the charges by saying the action was “unjustified” and he acted in the “best interests of truth, transparency and investors”.
SEC chairman Jay Clayton said in a statement: “This matter reaffirms an important principle embodied in our disclosure-based federal securities laws.
“Specifically, when companies and corporate insiders make statements, they must act responsibly, including endeavouring to ensure the statements are not false or misleading and do not omit information a reasonable investor would consider important in making an investment decision.”