Could it be that Doctor Octopus, affectionately abbreviated to Doc Oc, could be more powerful than The Hulk? Seems preposterous since Hulk has unmatched strength and indestructible skin, yet somehow Doc Oc somehow gets the upper hand on who Spider-Man calls “Lettuce Lips”. We get to see an example in Spider-Man issue 19, which is part 2 of the Story arc Revenge of the Sinister Six. It is Doctor Octopus vs Hulk, one monster against another.
From the previous issue, Spider-Man has been watching from the shadows as Sandman, as well as other villains, confront Doctor Octopus about his plans. All of them combined cannot touch him because he has unbreakable adamantium arms with a limitless power source. These arms allow him to battle all of them at the same time. After Doc Oc turns Sandman into glass with a special weapon, Spider-Man decides to intervene. Unfortunately The Hobgoblin uses gas on Spider-Man that knocks out his spider-sense, making him vulnerable to attack.
Right on time, The Hulk explodes through the wall dramatically to save the day. He is there because the Delphi from the group Pantheon used her precognitive abilities to foresee Doctor Octopus taking over the world. Shocker tries to stop Hulk but he just flicks him away with his finger. Doc Oc manages to grab Spider-Man’s leg and bashes him all around, destroying his costume and throwing his body into the harbor. Now it is just Doctor Octopus vs Hulk, as Hulk easily took out all the Villains. Hulk thinks that Doc Oc is still physically a normal man, and one blow to the head should end the fight. Hulk dives at him from behind while Shocker recovers and shoots a blast above him, casting a telling shadow over Doc Oc. The response is one of his mechanical arms grabbing hulk by his neck, and his other arms lifting him up off the ground in restraint. Doc Oc then proceeds to hit Hulk repeatedly with his arms as blood slings everywhere. Finally he is thrown away so that the Sinister Six can escape the police.
It is rather surprising that when we see Doctor Octopus vs Hulk that the invulnerable beast of a creature is no match to adamantium mechanical arms. Your best bet to reading this story arc (Affiliate Link) is to pick up the graphic novel version, which happens to be available in hard cover format.