Cape Town - Manchester United defender Luke Shaw admits they have squandered the chance to build upon the wins over their top-six rivals by failing against other teams.
The Red Devils enjoyed successes against Tottenham and Manchester City earlier this month but followed that up by drawing at home to Everton and then slumping to a miserable 2-0 defeat at bottom club Watford on Sunday.
The loss at Vicarage Road leaves United seven points adrift of the top four heading into the Christmas period.
Ole Gunnar Solskjaer's side have struggled against opponents who sit deep, winning just one of the last 17 games when they have enjoyed more possession.
In-form Newcastle, who beat United 1-0 at St James' Park earlier in the season, are the visitors to Old Trafford on Boxing Day and Shaw is calling for improvement ahead of the game.
"We need to be better and we know we need to be better," he told manutd.com.
"The wins against Spurs and City were great but now they seem pointless with the last two results we've had, because we need to be beating the teams below us as well. We haven't done that.
"We will work on the training pitch and hopefully have a good Boxing Day."
Watford took the lead as Ismaila Sarr's tame effort slipped through the grasp of David De Gea, the United goalkeeper's sixth error leading to a goal since the start of last season.
But, after Troy Deeney's penalty four minutes later secured a first home win of the campaign for the Hornets, Shaw backed his team-mate to bounce back immediately.
"Of course, it was a freak goal," he added.
"David has saved us so many times in so many different matches over the years he has been here.
"There is no way you can point any blame at him at all. He is a world-class goalkeeper and I am sure he will pick himself up."