LeBron James Trolls Stephen A. Smith With Old Boxing Training Video

7:27 AM PT -- We knew this was coming -- Stephen A. Smith opened Thursday's "First Take" going off on LeBron ... saying his nemesis' real issue stems from the fact he refuses to consider him the greatest NBA player over Michael Jordan.

Smith made it clear he's never going to back down from his stance ... and he's not going anywhere.

As for his colleague Pat McAfee giving his rival a platform, SAS doesn't blame him one bit -- saying no one would pass up on an interview with James.

Smith also addressed James' trolling with his boxing vid ... and he even admits it wasn't his best work, but claimed he would've looked much better if he wasn't injured at the time.

LeBron James hit the game-winning shot for the Lakers on Wednesday, but the real dagger came on Instagram later in the night ... when he ruthlessly clapped back at Stephen A. Smith AGAIN by mocking his fighting skills.

The King added another chapter to the beef after L.A. beat the Indiana Pacers ... clearly getting wind of the ESPN host claiming earlier in the day he would've "swung" on the four-time champ if he had put his hands on him during their Crypto.com Arena confrontation a few weeks back.

Even though SAS admitted it probably would've resulted in getting his ass whooped, LeBron made sure the talking head knew how he felt about the comments ... sharing an old video of one of his boxing sessions, which didn't necessarily mimic a Ryan Garcia left hook.

"🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣 WHOMP WHOMP WHOMPPPPPPPP," James said in his Instagram caption ... and countless fellow athletes -- from Kevin Love to Tristan Thompson to Draymond Green and Paul Pierce -- added insult to injury in the comment section.

Of course, both sides have been chirping quite a bit following their altercation -- Stephen A. claims Bron's spewing lies about what it all stems from, but the 40-year-old insists he was simply defending his family after the "First Take" talent crossed the line with his coverage.

As for the action on the court, LeBron hit a clutch put-back off Luka Doncic's miss to help the Purple and Gold beat the Pacers on the road ... with the Lake Show winning the contest, 120-119.