The connecting record
statedOne Punch Man · ch. 72, pp. 8-12
Monster King Orochi beat Gouketsu in One Punch Man.
Off the page, before the story opens. Gouketsu lost, and was kept alive on condition that he ate a monster cell.
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 · Gouketsu · rank 10
Won the first Super Fight tournament as an ordinary human eleven years before the story opens, was beaten by Orochi some time after that, and swallowed a cell instead of dying. Came back to the stadium that had made him and put the same offer to the field: eat one or be killed. Five of them ate. He was the demonstration of what the bargain costs, and it cost him his head on the road out of town.
statedOne Punch Man · ch. 72, pp. 8-12
Won the first Super Fight tournament as a human, lost to Orochi, and accepted a monster cell in exchange for his life.
shownOne Punch Man · ch. 66, p. 24
Smashes Genos into the pavement with a single blow on his way to the stadium.
shownOne Punch Man · ch. 71, pp. 40-42
Orders every martial artist in the stadium to eat a monster cell and become a Mysterious Being.
All 7 citations
shownOne Punch Man · ch. 72, pp. 2-23
Rosie, Choze, Benpatsu, Volten and Hamukichi take the cells and transform in front of him.
statedOne Punch Man · ch. 74, p. 10
Says he is far weaker than Orochi, whom he calls the strongest Mysterious Being in the world.
shownOne Punch Man · ch. 75, pp. 30-36
Lands at least two blows on Saitama to no effect, and his head is removed and lands in the stadium.
statedOne Punch Man · ch. 69
Monster cells first appear here; they are a manga addition with no webcomic counterpart.
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.