The Red Bull driver, under pressure after a run of poor form, tried to pass around the outside but made contact and was pitched up and onto the run-off with sidepod damage. He got his car back to the pits where he retired.
"I am aware that I took a big risk today but I forgot about the championship and I forgot about everything else, I was only thinking about winning today," Perez told reporters.
"I didn't think that Leclerc was going to brake so late because he was in the middle and I had already passed him, I didn't expect him to be there.
"For me a podium in Mexico would not have been enough, today I wanted to win and when I had the chance I risked it and maybe risked too much, but I would do it again," added the Mexican.
The race drew a record three-day crowd of 400,639, according to Formula One, with most of them coming to cheer a home hero who said before the weekend that it was his most important of the season.
Perez had stood proudly at the singing of the national anthem but the cheers were soon replaced with tears of frustration.
The Red Bull driver made a quick getaway from fifth and attacked Leclerc on the outside as triple champion Max Verstappen went past the Monegasque on the inside.
Leclerc, who finished the race in third place and was booed afterwards, said he was left with "nowhere to go".
"I was a bit in between the Red Bulls and unfortunately I touched Checo. It's life. I damaged my car and unfortunately it ended the race of Checo," he said.
Red Bull boss Christian Horner said it was a racing incident.
"You can't blame him (Perez) at his home race for trying to get into the lead in the Grand Prix. It's a tough moment for him in front of his home crowd, he is very emotional," added the Briton.
Perez remained second in the championship standings but with his lead over Hamilton slashed to 20 points.
Horner said finishing second overall was not make or break for the Mexican, who has a contract for 2024, to be with the team next season.
"He's had some misfortune and issues but we still believe he can do it. Our attention is to get him in the car for 2024, we want him to finish second but if he doesn't that's not a prerequisite," he said.
The team and Verstappen, who claimed a record 16th win of the season, have already won both championships.
