Investors betting against Elon Musk's electric-auto maker Tesla collectively lost an estimated $1 billion-plus on Thursday as the company's stock headed for its best day on Wall Street since 2013.

Tesla popped 16.5% Thursday to around $300 per share, meaning short sellers betting against the stock are on track for $1.4 billion in mark-to-market losses on the day — wiping out almost 70% of short sellers' year-to-date profits, estimates S3 Analytics.

"Short sellers are, as Elon Musk stated earlier in the year, 'feeling the burn,'" wrote Ihor Dusaniwsky, managing director at S3. "Prior to today's price move TSLA short sellers were up +$2.00 billion in mark-to-market profits, this is down from its year-to-date P/L high of +$5.16 billion of mark-to-market profits before TSLA began its sustained rally in June."

To be sure, those who bet against Tesla at the start of 2019 are still in the black to date with the equity down more than 11% this year after Thursday's price moves. Tesla stock closed at $254.68 on Wednesday, which at the time represented a 23.4% slide for 2019.