San Diego's MLB team tapped the "Jackass" star for the pregame ceremonies at Petco Park just before the Friars took on the Royals ... and, in true Steve-O fashion, he wowed everyone in attendance.

The 48-year-old stuntman hit the field with a custom No. 62 "Steve-O" Padres jersey and a flaming glove ... before he spat a liquid that set ablaze above him.

Check out footage from the diamond -- the flames were nearly as tall as him!!

The entertainer then put the ball into the fire ... before he chucked it to San Diego's mascot at home plate for a perfect strike.

Steve-O was clearly fired up (sorry) over it all ... 'cause afterward, he gloated about the moment on his Instagram page.

"My first time throwing the first pitch at an @mlb game— I’m pretty sure it’s never been done like this, too!" he wrote. "Thanks so much, @padres!!!"

The Padres were stoked over the stunt too ... tweeting, "Yeah, dude Thanks for stopping by and throwing out an epic first pitch."

Steve-O's first pitch was a sign of good things to come for the home team ... the Padres shut out Kansas City, 4-0, and Michael Wacha brought the heat on the mound, striking out 11 batters in seven innings.