Individual errors left West Ham with a mountain to climb against Swansea, Chris Coleman told Sky Sports.
Errors from Jussi Jaaskelainen and James Collins in the first half gifted the hosts a 2-0 lead and they capitalised on that advantage by adding a third in the second period.
That's two wins from two for the Welsh side this season and Coleman says the Swans are looking good.
"Swansea came into this game with a lot of confidence after scoring five goals against QPR last week," said the Wales boss.
"I expected a bit more from West Ham but I think their heads dropped when they gifted them the two goals in the first half.
"Obviously Sam Allardyce came here with a game plan but your game plan doesn't matter if you're going to give goals away and make errors, especially against this Swansea City side at home.
"In the second half West Ham had to open up to try and get a goal back and, in doing so, they left themselves open for Swansea's third.
"Swansea love it when the game opens up. They want to play through the middle and they could have scored more."
Angel Rangel opened the scoring with a cross-shot squeezing under the Hammers keeper and Dean Ashton said: "Rangel wasn't intending to shoot but Jaaskelainen made a bad error and, early on in the game, that put West Ham on the back foot.
"The second goal was a good finish from Michu. It was a dream for him to be handed a goal like that. But Michu is anticipating there's going to be a mistake, which you should do, and produced a good finish to slot it in. He's made a great start to his Premier League career - but James Collins will be really disappointed.
"And it was important for Danny Graham as a striker to get his first goal. He had a one-on-one before this, which he missed and would have been disappointed about, but he anticipates Wayne Routledge's cross and produces a good finish. He'll be really pleased to get off the mark."