ATGs in their prime in fights that they looked very ordinary

[Controversial]

As the question says, an ATG fighter, in their prime years but looked very poor or struggled with someone they shouldn’t have. Not fights they necessarily lost but maybe won and just looked awful or very average.

[goose 5]

Robinson's draw with Henry Brimm- based on what I've read.

[Ambling Alp II]

Just some off of the top of my head:

Joe Louis in the first fight against Conn looked way off until the end.
Hagler vs Marcus Geraldo
Mayweather vs Castillo I

[Expug]

Good topic. There are a lot of these. Especially back when there were non title fights.
Alexis Arguello dropped a ten rounder to Vilomar Fernandez when he was champ.

[Seamus]

Willie Pep's first bout with Jimmy McAllister. Pep was 8 days rest while McAllister was on 77, but it was still an off night for Pep who went back to normal for his 2nd and 3rd fights with Jimmy.

[gilgamesh]

James Toney against Dave Tiberi had a mediocre performance.

Whitaker had a bad night against Diobelys Hurtado. He pulled it out of the fire with a dramatic come from behind KO, but he'd had a bad night most of the fight.

[gilgamesh]

Hagler getting by Duran by the skin of his teeth isn't a particularly great performance on his part. Good, competitive fight though.

[Ambling Alp II]

Willie Pep's first bout with Jimmy McAllister. Pep was 8 days rest while McAllister was on 77, but it was still an off night for Pep who went back to normal for his 2nd and 3rd fights with Jimmy.

When you fight that often, you are bound to have the occasional off night. Moore occasionally had performances like that as well.