Rafa Benitez's side got off to the perfect start when Ritchie tucked away a penalty after being fouled in the box early on, before Murphy added a second on 32 minutes.

Huddersfield fought back, and Aaron Mooy's penalty gave them a glimmer of hope after the break at the John Smith's Stadium.

But substitute Gayle - brought on as a substitute on his comeback from a hamstring injury - tapped home into an empty net in added time to seal the win for the Magpies.

Though the hosts started brightly, it was Benitez's men who registered the first shot on goal. Mo Diame's driving run created an opportunity for Murphy, but the Irishman's drive was tipped over by Danny Ward.

And when the Terriers failed to properly clear their lines from the resulting corner, United took the lead. Ritchie was felled by Bermudan forward Nahki Wells on the left-hand side of the box, and referee Roger East showed little hesitation before pointing to the spot. Scotland winger Ritchie stepped up, confidently sending Ward the wrong way to give his side a tenth-minute lead.

At the other end, Karl Darlow was called into action for the first time midway through the half, palming away Philip Billing's fierce strike from distance as David Wagner's play-off chasers demonstrated their intent.

But the Magpies remained resolute, and doubled their lead just after the half hour. Jonjo Shelvey floated a delicately-weighted through ball over the Town backline, which Murphy looked to have miscontrolled. His persistence showed, though, as he reclaimed the ball from Ward - who had attempted to dive on it - and turned before cleverly steering the ball into the net from a tight angle to delight the almost 2,000-strong travelling band of supporters.

Chris Lowe then fizzed a shot wide and Izzy Brown tested Darlow, before the ex-Nottingham Forest stopper produced an eye-catching stop to turn Aaron Mooy's effort past the post as the Terriers showed some bite before the break.

Young midfielder Billing blasted over and then failed to connect properly with a volley after Wells' knock-down as Wagner's side rallied once more at the start of the second period.

And with the hosts having enjoying much of the play since the restart, they eventually got a chance to pull one back in somewhat fortuitous circumstances. Referee East adjudged Elias Kachunga to have been brought down in the box, and Mooy slotted away the resulting spot-kick to set up a nail-biting last 18 minutes.

They continued to pile on the pressure, with Kachunga firing into the sidenetting, but with just a few minutes of added time remaining, Gayle - on in place of Murphy - netted his 21st of the season to make the points safe.

With goalkeeper Joel Coleman, himself a substitute, retreating having made his way upfield for a corner, a long ball over the top from Ciaran Clark was misjudged by the Terriers custodian, and Gayle pounced to apply the finishing touch and round off another memorable away day for United.