After individual defensive mistakes ensured the Baggies lost their unbeaten home record, Greening insists that nobody at The Hawthorns should be feeling downbeat.
The Baggies now sit four points behind leaders Watford but can close the gap to a point on Saturday.
"You can't give two sloppy goals away like we did in the first 12 minutes," said the skipper.
"After that we were struggling to get back into the game because they had a two goal lead and just tried to frustrate us.
"The gaffer had a right go at us at half-time for the two sloppy goals we gave away and told us we had nothing to lose to try and get back into the game.
"We did really well to get back to 2-2 but then the sending-off changed the game really.
"I haven't seen a reply of the sending off but Robbo says he touched the ball first and he feels really hard done by.
"If we'd kept 11 men on the pitch we probably would have go onto win the game because we were the better side in the second half.
"But, after having a man sent-off, we should have concentrated more and held out for the draw."
Greening also revealed the disappointment Leon Barnett expressed after his costly error in the build-up to the third goal.
"Leon's upset with himself because he knew he should have launched the ball up the field and then they don't score their third goal.
"We've got to learn from these mistakes," Greening added.
"We've been quite strong defensively lately and to give stupid goals away like that is gutting.
"It's our first loss in a while though and we need to bounce back on Saturday and try to get the three points.
"We've got to put this defeat to bed straight away and work on our shape for Saturday."