Matic made the brave decision to swap Stamford Bridge for Old Trafford in the transfer window, joining Jose Mourinho's side for £40 million.
He's made a decent start to life up north and formed a particularly strong partnership with Paul Pogba in midfield.
But against Chelsea he was completely dominated by his former teammates, namely the indefatigable N'Golo Kante and his long-term replacement, Tiemoue Bakayoko.
Matic and Ander Herrera struggled to cope with the energy and power of Chelsea's midfield, who enjoyed 54% of the possession.
United remain above Chelsea in the Premier League and are still the more likely to challenge Manchester City for the title, but Matic will have hoped for a more successful return to the Bridge.
There was one moment in the game where the Serbian was punished for leaving Chelsea for a title rival, and unsurprisingly it involved Eden Hazard.
Hazard was nigh-on untouchable against United, despite Mourinho ordering his players to man mark the Belgian.
Footage has now emerged of Hazard showing his strength and skill to sit protect the ball from Matic and then sit him down by bursting away. Check it out.
That's what you get for leaving, Nemanja.
Matic is a 6ft 4in midfield powerhouse, yet he could get nowhere near Hazard, who is much shorter but really strong for someone of his size.
Chelsea fans were initially concerned about losing Matic to United over the summer, but Kante and Bakayoko's blossoming partnership has proved they had nothing to worry about.
Joey Barton echoed that sentiment on Monday when he said on talkSPORT that Kante's performance showed why they don't need Matic.
"I think in the last few weeks, having Kante out, the [Crystal] Palace result not going great, but the loss of Kante was huge because he's an incredible player," said Barton.
"They spoke about how Matic was seen as a big drop ball by the Chelsea hierarchy to let him go to Manchester United and I don't think Bakayoko has been sensational.
"But Kante proved yesterday why they did that."