David Luiz received his first Premier League red card for a high challenge on Sead Kolasinac with only three minutes left in Sunday's Premier League contest.
But Conte felt referee Michael Oliver should have already blown up before David Luiz's infringement after a challenge from Gunners substitute Sanchez.
Conte told Sky Sports : "David Luiz, you know very well that I don't like to comment about the referee. I didn't do this it in the past and I don't do it in the present.
"The only thing I can tell is you need to see what happened before the tackle."
Asked if perhaps there was a foul on Luiz before he fouled Kolasinac, Conte answered: "Yeah."
Conte went on to discuss the issue again in his post-match media conference and insisted he was certain Sanchez should have been penalised for his challenge on David Luiz, which prompted the Brazil international to lose possession.
"For sure, that was a foul," he said. "For sure. But, I repeat, the referee took this decision. If he stopped the play before, it [Luiz's challenge] wouldn't matter.
"I repeat, in this situation a player is fouled in a continuing way – he continued to push him."
Conte was unsure if Chelsea would appeal the decision, adding: "We have to wait for the referee's decision to know how many games he will be suspended for.
"We have great respect for them [officials], but it is very strange to finish a third game in a row against Arsenal with 10 men."
As well as the run of reds against Arsenal, Chelsea have had three sending offs in five league matches this season, Gary Cahill and Cesc Fabregas having been given their marching orders against Burnley on the opening weekend.
"I was a player and I think it can happen, this type of period, if you are not so lucky and receive red cards," Conte added.
"But, as I said before, I think we have to try to improve in all situations. We work to improve tactical and physical situations.
"In the end, we'll try to pay more attention in the future. I hope, also, to be more lucky with the refereeing decisions. For us, and also for the opponents.
"Sometimes the opponents deserve a red card but, instead, they carry on playing with 11 men."