Martin Jol's side were well beaten at Upton Park, and Parker offered an honest assessment after the game.
"I'm very disappointed, because it's a bad result and they're obviously key," Parker told Sky Sports News.
"We knew it would be tough, but we come here thinking we could get something you know. I thought they put us under pressure at times but we had a threat going forward, so we're disappointed as I say.
"We did try to push on to get back into it, so we're unhappy with conceding the other two late on."
The defeat leaves Fulham in the relegation zone in the Premier League.