The connecting record
shownOne Punch Man
Saitama killed Gouketsu in One Punch Man.
Head removed on the road out of C-City; it came down inside the stadium the monster had just emptied.
What each of them is ranked on
The killer · 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.
The victim · 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 death in one work. It is the only place the record puts these two in the same room, 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.