The connecting record
shownOne Punch Man · ch. 94, pp. 72-73
Monster King Orochi beat Garou in One Punch Man.
Garou is knocked unconscious and kept alive on Gyoro Gyoro's orders; he is later found chained underground.
What each of them is ranked on
The winner · Monster King Orochi · rank 9
Head of the Monster Association and the thing its sacrifices were feeding. Blown apart underground and still conscious afterwards, he dragged himself back together out of other monsters' blood, tried to swallow the woman who had made him, and came out of that merger holding a share of "God's" power. Twenty-nine chapters passed between the punch and the body finally stopping.
statedOne Punch Man · ch. 74, p. 10
Gouketsu calls him the strongest monster on Earth.
statedOne Punch Man · ch. 114, p. 13
Psykos says she cannot gauge his power and calls him a real monster.
statedOne Punch Man · ch. 115, p. 7
Already knowing Saitama beat Overgrown Rover, and sensing the pressure off him, works out that he also beat Gouketsu and Elder Centipede.
All 8 citations
shownOne Punch Man · ch. 131
Survives being blown apart by Saitama and regenerates by absorbing the blood of other monsters.
shownOne Punch Man · ch. 132, pp. 9-12
Attempts to absorb Psykos and the two end up sharing one mutated body.
statedOne Punch Man · ch. 136, pp. 16-20
"God" appears during the merger and adds power to the fusion.
shownOne Punch Man · ch. 136, pp. 7-13
The fusion's attack cuts through the Earth's surface and lifts a severed disk of oceanic crust, seawater and the sky above it.
shownOne Punch Man · ch. 160, pp. 44-45
What is left of the body is used as a sacrifice to resurrect Sage Centipede.
Beaten · Garou · rank 2
Hero Hunter
Put down the S-class hero Tanktop Master, and had Metal Bat bleeding and broken and about to be finished when the hero's sister walked in and stopped it — both while still an unenhanced human, having been thrown out of his master's dojo months earlier for hospitalising the rest of the students. After contact with "God" he copied Saitama's striking power outright, and the pair of them had to be moved off the planet before their fists met, with the released energy pushed away from Earth by four people afterwards.
shownOne Punch Man · ch. 47, pp. 11-14
Beats the S-class hero Tanktop Master after a barrage of punches.
shownOne Punch Man · ch. 58, pp. 32-40
Dodges and deflects everything the S-class hero Metal Bat throws, moving faster than Metal Bat can follow.
statedOne Punch Man · ch. 30, p. 5
Bang says he beat Garou and expelled him from the dojo after Garou disabled the other students.
All 10 citations
statedOne Punch Man · ch. 81, p. 17
Tells the heroes ambushing him that he has beaten close to a hundred of them.
shownOne Punch Man · ch. 77, pp. 17-20
Watchdog Man beats him and drives him out of Q-City.
shownOne Punch Man · ch. 169, pp. 53-55
Takes on Cosmic Fear Mode after contact with "God".
shownOne Punch Man · ch. 173
Withstands repeated Serious Punches and keeps fighting until Saitama's output outgrows him.
shownOne Punch Man · ch. 172, pp. 3-10
His Serious Punch collides with Saitama's, and Blast and three others divert the released energy away from Earth.
statedOne Punch Man · ch. 171
Blast warns him that in this state anything he does could end life on Earth, and he is unbothered.
statedOne Punch Man · webcomic ch. 55, p. 1
The webcomic also rates him a Dragon-level threat.
What this does not settle
One fight in one work. It is the only result the record gives between these two, and it is evidence about that meeting and nothing wider — not a general matchup, not a rematch, and not a ranking of its own.
The ladder above it is argued from everything either of them has been shown doing; this page is argued from one citation.
Where the two disagree, the disagreement is the point, and it stays visible rather than being resolved by whichever of them happens to be on this page.