Record 11-times winners United were stung by Dirk Kuyt's late winner which earned Liverpool a dramatic 2-1 FA Cup fourth round victory over their bitter rivals at Anfield on Saturday.
But champions United remain just three points behind Premier League leaders Manchester City and South Korea midfielder Park, speaking ahead of Tuesday's league match at home to Stoke, insisted United they could not afford to dwell on the Liverpool defeat.
"We must quickly forget about this game, move on and look to the future," Park told Manchester United TV (MUTV). "We still have the Premier League and the Europa League to focus on."
United are entering a critical spell.
After Stoke, they face a huge game at fourth-placed Chelsea on February 5 before entertaining Liverpool in the league six days later.
Then Sir Alex Ferguson's side, who failed to advance past the group stages of the Champions League, face a tricky two-legged Europa League tie with Ajax.
Park added United must not lose concentration as they did at Liverpool.
"We controlled the ball which is what we wanted before the game," he added. "We did that well but that couldn't get the win for us.
"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."
Ferguson was missing several key players at Liverpool due to injury including England striker Wayne Rooney, Portugal winger Nani and defender Phil Jones.
It remains to be seen whether the Stoke game will come too soon for any of them but England defender Rio Ferdinand could return from a back injury.
"Rio only had one training session ahead of the Liverpool game," said Ferguson. "We couldn't gamble with that.
"He will train on Sunday and Monday. He could be right for Tuesday."
Stoke will head to Old Trafford with only two defeats in their last 12 games and boosted by the recent draw at Anfield.
Tony Pulis, the manager, made only four changes from the team that lost to West Brom in the Premier League the previous weekend for Saturday's FA Cup win at Derby and will juggle his squad again.
And winger Jermaine Pennant is on a mission to pile more frustration on Ferguson, after United's late choker against Liverpool.
"They are coming off the back of a disappointment against Liverpool so they'll be fired up and Old Trafford's never an easy place to go," Pennant said.
"But on the day they are beatable --- Blackburn proved that. So if we go there, with our style of play, with a bit of physicality, hopefully we can dominate that side of the game and you never know, we'll see what happens.
"We'll go there positive. A lot of teams go to Old Trafford already beaten, before they've got on the pitch, so we'll get that out of our minds straight away and as soon as that whistle goes, know that anyone can win.
"Look at our record against the big teams -- we've beaten Liverpool at home and drawn with Chelsea and United -- we do seem to do well against the big teams.
"If we can go there with the same attitude and mentality, hopefully we can come out with a positive result."