The Liverpool substitute latched on to an Andy Carroll flick-on, after being left unmarked, before firing past David De Gea to seal a 2-1 fourth round victory for Kenny Dalglish's men. Park, who netted United's equaliser just before half-time, says the Reds felt particularly disappointed at the final whistle after dominating much of the possession.
"We controlled the ball which is what we wanted before the game. We did that well but that couldn’t get the win for us," the Korean told MUTV. "In the team meeting, we talked about trying to keep possession and then make chances. We did that and that’s why we played very well.
"But then we lost concentration for a moment and ended up giving them the goal to make it 2-1. Everyone was quiet afterwards because we all feel disappointed."
As always in the aftermath of defeat players can't wait for the next game and United don't have long to wait with an important Barclays Premier League clash against Stoke to come on Tuesday at Old Trafford. Vital league matches against Chelsea and Liverpool follow early next month with the latter stages of the Europa League also due to start.
"We must quickly forget about this game, move on and look to the future," insists Park. "We still have the Premier League and the Europa League to focus on."