Three goals in the final 20 minutes, two struck by the hosts, saw the Hammers edge this five goal thriller.
“We’re angry and disappointed. We feel like we’ve let one slip today,” Parker said afterwards.
“For 30 minutes we were excellent and deservedly went a goal up. We nullified any of their threats and we were well on top.
“But from the moment we scored, we lost focus and turned it into a basketball match, end to end, which suited them more than it did us.
“We fell short from a set play just before half time and that gave them an avenue back into the game.”
Parker also lamented: “In crucial moments, there was a lack of concentration. We fell a bit short in certain moments.
“There were nice bits in the second half again, but we gave them another poor goal. We lacked a bit of nous in those moments.
“There’s stuff that is costing us at the moment and it’s up to us to fix those things.
“We’re all leaving here thinking we’ve missed an opportunity - that’s the big frustration.”