Screen Rant

Why was Iron Man, in the Hulkbuster suit, able to beat the Hulk in Avengers: Age of Ultron? 1 / 8

This was because Tony knocked The Hulk out at the end of the fight, before The Hulk could summon his rage, which gives him strength. 2 / 8

The Hulk and Iron Man had just fallen through a building, allowing Iron Man to knock out the disoriented Hulk. 3 / 8

With The Hulk having a momentary gap in his rage, this allowed Iron Man to punch him when The Hulk was vulnerable. 4 / 8

Iron Man and The Hulk had an explosive fight in Age of Ultron... 5 / 8

But in the end, The Hulk lost due to Iron Man landing a punch at just the right moment. 6 / 8

The Hulk also needed The Grandmaster's help against Thor in Thor: Ragnarok... 7 / 8

And he was badly beaten by Thanos in Infinity War, so he's had later MCU fights that didn't go as he'd planned, too. 8 / 8