Well before the end visiting fans began imploring David Moyes to give them a wave. How Manchester United's manager must wish it were this easy every week – and how Alan Pardew could do with the season ending now.

As the bulk of the side Moyes will field in the Champions League tie at Bayern Munich on Wednesday rested their legs, the excellent Juan Mata scored twice and Javier Hernández and Adnan Januzaj once apiece. In between there were some lovely cameos from the technically assured Shinji Kagawa and Newcastle supporters were left wondering how on earth their team remain ninth.

With the Tynesiders having failed to score in 11 of their past 15 league games, Pardew must suspect he cannot survive too much more of this. The past three fixtures alone have seen 11 goals conceded and none scored. Admittedly, he has not been properly backed in the transfer market and is coping with a mini injury crisis but this was the sixth game since the start of February that Newcastle have surrendered by a three- or four-goal margin. Small wonder Pardew admits he is struggling to motivate a group of players who appear to be mentally on the beach.

"Disappointing," said Pardew. "We just couldn't get into the game. There's no doubt we're lacking a bit of cutting edge. We've been losing heavily and Stoke away next weekend is a big game for us now. I understand the fans' frustration. We're just not producing exciting football. United were too good for us today. Our last three games have been tough, tough, tough."

Despite their own travails at home Moyes's team recorded their biggest league win of the season and now boast the division's best away record. "We were very good," he said, before singling out Mata, Kagawa and Darren Fletcher out for special praise. "There's a bit of expectation at Old Trafford, a bit less pressure away. We've lost a few home games after being a bit gung ho."

Goodness knows what damage Moyes's team might have inflicted had Wayne Rooney – whose toe injury looks set to heal in time for Munich – been playing on a day which began in deceptively underwhelming fashion. There was an early reminder that Ashley Young's crossing can be surprisingly poor as Moyes's second stringers enjoyed quite a bit of possession without initially doing too much with it. Marouane Fellaini certainly did not look a £27m midfielder and was arguably fortunate not to be sent off for a nasty elbow on Dan Gosling.

Young swiftly departed nursing a dislocated thumb, his place going to Januzaj. By now the crowd were receiving a reminder that since Yohan Cabaye's defection to Paris Saint-Germain, a less-than-inventive Newcastle have become, as Pardew concedes, "functional". Whacking too many optimistic balls from back to front and proving extremely narrow in midfield, they definitely looked it here.

In mitigation, Loïc Rémy, Mathieu Debuchy, Tim Krul and Moussa Sissoko were all absent, injured, but, equally, this was a far from full-strength Manchester United. Tellingly, after falling behind, Newcastle never really looked like salvaging even a point. That critical first blow was struck when Gosling fouled Fletcher late outside the penalty area. Mata – ineligible for the Champions League – stepped forward to take the free-kick and his exquisite delivery curled irresistibly into the top corner. It arguably represented the Spaniard's best moment since leaving Chelsea.

Moyes should swiftly have been celebrating a second goal after Kagawa's pass to Hernández bisected the home defence but both striker and his manager were left holding heads in hands after his ensuing shot rebounded off a post with Rob Elliot beaten. No matter: early in the second half Kagawa and Hernández combined cleverly and when the latter sold the defence a dummy, Mata delighted in deceiving Fabricio Coloccini. With Elliot similarly tricked he rolled the ball in from close range.

It was the cue for Hatem Ben Arfa's belated bow as the replacement for Newcastle's wholly ineffective Luuk de Jong. He finally provided the visitors with a few frights but, exploiting Newcastle's need to chase the game, Hernández soon made it three. This time Januzaj and Kagawa shared the job of bewildering the Newcastle defence before Hernandez's tightly angled left-foot shot crept beneath Elliot.

By the time Januzaj slipped number four beyond Krul's deputy – courtesy of Mata's adroit backheel – a few near misses on Papiss Cissé's part had failed to prevent significant anger festering in the stands. It expressed itself in loud, prolonged booing at the final whistle.

At least Moyes now knows he is not the only manager with problems.