West Ham manager Sam Allardyce rued the two defensive mistakes which helped Swansea cruise to a comfortable 3-0 victory against his newly-promoted Premier League side.
The Swans went ahead when experienced Hammers goalkeeper Jussi Jaaskelainen allowed Angel Rangel's low cross to slip underneath him.
And moments later Michu doubled the Welsh side's lead when he seized upon centre-back James Collins' mis-kicked backpass.
It was a disappointing afternoon for Allardyce and his troops, who marked their top-flight return with a 1-0 home win against Aston Villa on the opening day.
"We made two very poor mistakes by our two most experienced players on the field which cost us dearly," said Allardyce. "These mistakes were punished by Swansea.
"I'm disappointed because we got a good solid base last week and it looked apparent to me we were in control again.
"We were under no pressure but to make those mistakes, at this level, is unbelievable.
"We made things hard for ourselves. Our performance overall in the first half, apart from those two mistakes, was very good."