A parking lot of predominantly new Tesla Model 3 electric vehicles is seen in Richmond, California, U.S. June 22, 2018.

"While Inside EVs' estimates are just that, estimates, we believe the service has been effective in identifying directional and order of magnitude trends on monthly shipments for Model 3 in lieu of verified data from the company," analyst Colin Rusch said in a note to clients Thursday. "We believe TSLA is tracking toward achieving its 3Q:18 guidance."

Tesla shares closed slightly higher Thursday after CEO Elon Musk tweeted that the company was "1st, 2nd & 3rd in August sales," pointing to a report by InsideEVs.

The firm reiterated its outperform rating for the electric car maker's shares, citing strong third-party August sales estimates.

Oppenheimer believes Telsa will meet its third-quarter targets for Model 3 production and profitability.

Rusch reiterated his 12-18 month $385 price target for Tesla shares, representing 37 percent upside to Wednesday's close.

Previously, Tesla gave production guidance for the third quarter of 50,000 to 55,000 Model 3 cars and a gross margin of "roughly" 15 percent for the vehicle.

The analyst noted that InsideEVs estimate for second-quarter Model 3 deliveries was 18 percent below the actual number the company reported. He said if Tesla consistently produces 4,300 Model 3 cars per week, it can reach the high end of its guidance for the third quarter.

"We believe TSLA has the potential to be a transformational technology company and deliver outsized returns," he said.

Tesla did not immediately respond to a request for comment.

Note: InsideEVs reached out to CNBC to clarify that the Oppenheimer analyst's number included Tesla's Canadian deliveries, while their estimates are only for the U.S. As a result, the outlet's second-quarter estimate was not significantly off the mark.