The 23-year-old impressed on his debut before being dismissed in the 58th minute for a foul on Kenny Tete.
It was the turning point that put Chelsea on the back foot after they were pushing for an equaliser after Kalidou Koulibaly’s strike earlier in the half.
Speaking after Carlos Vinicius and Willian’s goals piled the pressure on his position as manager, Potter was frustrated once again.
“I don’t think it was an emotional one from Joao, it didn’t feel that to me,” Potter said. “It was a miscontrol and then just a football action that can happen with the speed of the Premier League and a game of football at this level.
“There was no malice, he didn’t go into hurt anybody, he didn’t lose his head, it just was what it was. Sometimes these things happen and they’re against you and you have to suffer.
“And believe you me, we are suffering at the moment.”
Mason Mount, Carney Chukwuemeka, Kalidou Koulibaly, Jorginho, Thiago Silva and Cesar Azpilicueta were among the players who went over to the fans after a run of three defeats in a row.
They acknowledged a furious fan base when several other Blues players didn’t, seemingly embarrassed about their own performances.
With his side tenth in the Premier League and six points behind their west London rivals, Potter urged unity: “Yes, but I can also understand they are frustrated because we’ve lost.
“That is normal. I made sure I went over and clapped to them because you appreciate the support. “It’s not easy. We’re suffering and they are suffering.
“So we feel for them and feel their disappointment. I think it’s important we stick together and try to get through this tough period because it really is a tough period.”