Declan Rice felt West Ham proved they are the real deal in the race for the Champions League in their 2-1 defeat at Manchester City.
The Hammers remain in the hunt for a top-four finish despite going down to a second-half John Stones goal.
Hammers skipper Rice told West Ham TV: "I thought you saw a different West Ham, one which was confident and really believed they could take it to City.
"We had so many good chances and it was one of those that when you come back to the changing room you're gutted. I'm hurt and I'm gutted we didn't come away with something.
"There were two or three times when we won the ball in their half and as soon as we did we'd give a sloppy pass away and they'd be back on it.
"They're the bits there we need to brush up on and it's so gutting to go there and not come away with a point. To have got three points would have been unbelievable but to not get at least a point was so unlucky.
"A year ago, we'd have a couple of games when we were good, then have games when we were poor, but now you can see our performances week in, week out – we're leaving everything on the pitch.
"You saw Vlad Coufal at the end with his hands on his head and the lads were gutted in the changing room. Something's really changed and things are improving."