Saitama vs. Genos

Even he cannot explain the secret to his strength... But this battle may afford me a clue! Saitama vs. Genos was a spar between Saitama and Genos.

Prelude
After Saitama and Genos had both passed the National Superhero Registry exam, they were placed last in their classes, with Genos being rank 17 in the S-Class and Saitama rank 388 in C-Class. Later, Genos thanks Saitama for accepting the request for a sparring match and asks Saitama to take it seriously. The motivation for this sparring match was to figure out the lengths Saitama's power.

Battle
Genos launches himself at Saitama but misses. He then follows up with a barrage of punches which Saitama dodges. Genos attempts to hit Saitama with his incineration cannon but misses. Genos tries to hit Saitama with another barrage of punches but is speed blitzed by Saitama as it turns out he was only chasing his afterimage the entire time. Genos tries to hit Saitama with a more powerful version of his incineration cannon, but Saitama easily evades it; taps Genos on the shoulder, pokes him in the cheek when he turns his head, and says that he wins. Genos retaliates by trying to punch Saitama, which Saitama avoids by jumping over and behind him. Genos then reminds Saitama that the rules of the fight involve him taking the fight seriously and continuing to fight until he is no longer able to. Saitama's legs tense slightly and he suddenly appears in front of Genos. Genos tries to kick Saitama; only for Saitama to flash step behind him. As Genos turns to face Saitama, Saitama's punch hurls towards him. Genos experiences impending death and can do nothing about it. Saitama stops his fist just before it hits Genos and all the force of the blow seems to travel around Genos. Saitama taps Genos on the forehead and says they should eat some udon.

Aftermath
Saitama's punch is revealed to have blown a hole through several mountains and clouds which form a canyon. Genos thinks he will never even come close to becoming as strong as Saitama.

Trivia

 * The battle lasted 4 minutes and 33 seconds, being Saitama's second longest battle after his fight against Boros.
 * In the manga, Saitama's punch does not blow a hole through the mountain behind Genos.