The connecting record
shownOne Punch Man · ch. 115
Saitama beat Monster King Orochi in One Punch Man.
Blown apart, not killed. Orochi survives, fuses with Psykos, is beaten down by the S-class heroes, and is finished by Tatsumaki.
What each of them is ranked on
The winner · Saitama · rank 1
Caped Baldy — Hero Association register
Aced every physical test at the certification exam and scored 71 out of a pass mark of 70, which put him at the bottom of the lowest class in the organisation. Punched apart the meteor falling on Z-City, killed the Deep Sea King in one blow in front of the heroes it had already gone through, and met a beam aimed at the Earth's surface with a Serious Punch whose shockwave parted cloud cover across the planet.
statedOne Punch Man · ch. 16, pp. 1-8
The certification exam awards him 71 points against a pass mark of 70 and a C-class designation.
shownOne Punch Man · ch. 16, pp. 1-8
Takes the physical tests at the exam centre in front of examiners and rival candidates.
statedOne Punch Man · ch. 17
Genos, reading the registry, says the two of them have been placed at the lowest rank of S-class and of C-class respectively.
All 11 citations
statedOne Punch Man · ch. 21, pp. 1-4
Genos tells him he has been moved from C-class rank 388 to rank 342.
shownOne Punch Man · ch. 21
Punches through the meteor falling on Z-City and walks away.
shownOne Punch Man · ch. 28
Kills the Deep Sea King with a single blow.
shownOne Punch Man · ch. 36
Repels Boros's Collapsing Star Roaring Cannon with a Serious Punch.
shownOne Punch Man · ch. 36, pp. 54-57 & 62-63
The shockwave off that punch parts the cloud cover across the whole planet.
statedOne Punch Man · ch. 36, pp. 68-69
Boros tells him he had strength to spare and was still holding back.
statedOne Punch Man · ch. 177, p. 37
Is promoted to A-class rank 39 after the Monster Association incident.
statedOne Punch Man · webcomic ch. 96, p. 16
The webcomic gives the same A-class rank 39 placement.
Beaten · 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.
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.