Marcos Rojo was lucky to escape with a yellow card for a studs-up tackle on Willian, according to Chelsea boss Maurizio Sarri.
The Argentine defender, who replaced the injured Eric Bailly for United in the second half, made two crunching tackles in a matter of seconds less than 10 minutes after coming on during the 1-1 draw.
First he clattered into Gonzalo Higuain before over stretching and catching Willian on the ankle with his studs.
Martin Atkinson only booked Rojo and Sarri believes the tackle was in between a yellow and a red, rather than a certain sending off.
"Willy was not happy. The card was an orange card, between a yellow and a red. We have to accept it. It’s not easy for the referee," Sarri said of the tackle.
There was controversy in the first half as well when Nemanja Matic caught Chelsea captain and his former teammate Cesar Azpilicueta with an elbow. Atkinson didn't penalise Matic for the incident and Sarri felt the Serbian didn't do it deliberately.
Juan Mata had given United the lead against Chelsea after 11 minutes, but the Blues equalised just before half-time when David de Gea spilled Antonio Rudiger's long-range shot, allowing Marcos Alonso to tap home.
It was the latest de Gea blunder to cost United, but Sarri defended the goalkeeper.
"It can happen. He’s a great goalkeeper, he’s unlucky in the last period, but the mistakes of a goalkeeper can happen," the Chelsea boss said.
"If I had to speak to De Gea in general he’s a very good goalkeeper, I have no doubts about it. Sometimes you have a striker who can't score for two months and sometimes you have a goalkeeper in difficult for three or four matches but this is the job of a goalkeeper, it’s impossible to stay at a very high level for 12 months with consistency.
"De Gea in my opinion is a great goalkeeper."
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