Longstaff, 19, started in Steve Bruce’s midfield alongside his brother Sean and scored the winning goal as the Magpies bagged a 1-0 victory at St James’ Park.
The Rotherham-born teenager struck the bar in the opening 45 minutes before scoring from outside the box in the second half and while speaking at the break, Redknapp shared just how pleased he was to see the youngster perform as well as he did.
“He’s won challenges, he’s protected the back-four really well, he’s kept it simple but he’s always had that long pass as well when it’s needed,” said Redknapp at on Sky Sports Main Event on Sunday [05:23pm].
“It’s not the best first-touch when it comes back to him but what it does it pops it up lovely so then he can hit that dipping volley and the strike is tremendous.
“He’s got a left foot, right foot. You can see he opens his body up really well and cuts across it slightly. Look at his brother there, willing this one in. It would have been such a great moment.
“His all-round game has been fantastic.”
Longstaff had a day to remember for the rest of his life on Sunday. The 19-year-old was handed his league debut for Newcastle, alongside his brother and against one of the biggest clubs in world football. Even before he kicked a ball it was a momentous occasion for the teenage midfielder but the fact that he did not look at all out of place against Man United suggests that Newcastle have some player on their hands here. It will be interesting to see whether Longstaff gets more game-time. The only reason he played on Sunday was due to Isaac Hayden being suspended and Jonjo Shelvey being injured but how does Bruce drop him now? Longstaff was arguably the best player on the pitch in the 90 minutes and it was one of the finest displays by a player in black and white stripes all season. If he does not start the next game after the international break then serious questions have to be asked.