In Amazing Spider-Man Vol. 1 #270, Spider-Man defeated Firelord, the former Herald of Galactus, who first appeared in Thor Vol. 1 #225 and was given his freedom by Galactus in Thor Vol. 1 #228.
The aftermath of the battle was shown in Avengers Vol. 1 #258, with Avengers such as the Black Knight and Hercules commenting on the extent of Firelord's power.
BLACK KNIGHT: Galactus, eh? I've met another of his Heralds... the Silver Surfer! If Firelord is even half as tough as the Surfer, Spider-Man must have put up the fight of his life!
HERCULES: I have battled both with and against Firelord... his power is awesome indeed!
Avengers Vol. 1 #258 (August, 1985)
The black costume worn by Spider-Man in this battle wasn't the alien symbiote he picked up during the original Secret Wars storyline, but a cloth replica made for him by the Black Cat, which he first started wearing in Amazing Spider-Man Vol. 1 #263.
SPIDER-MAN: The costume the Black Cat sewed for me! I almost can't believe that I'm putting this on! It looks just like the alien symbiote I brought back from the Beyonder's world!
Amazing Spider-Man Vol. 1 #263 (April, 1985)
In a much later issue, the Silver Surfer assumed Spider-Man was joking when he mentioned that he'd beaten Firelord once, apparently because he found the claim very hard to believe.
SPIDER-MAN: No idea, but we better figure it out fast. 'Cause there's hundreds coming. Possibly thousands. And they're all turning into your bad guys... which, no offense, isn't a problem for me. Heck, I took down the real Firelord once.
SILVER SURFER: I highly doubt that.
SPIDER-MAN: Honest! Firelord! Former Herald of Galactus! Boom! Pow! Knocked him out!
SILVER SURFER: I am sorry, Spider-Man, but your Earth humor escapes me sometimes.
SPIDER-MAN: I'm not joking! It was in all the papers. I--oh forget it. Don't know why I'm helping you. You're mean.
Silver Surfer Vol. 8 #6 (October, 2016)