Sanchez scored for the first time since January when he diverted home from close range with a diving header and registered an assist in the two-time defending Copa America champions' victory in Sao Paulo.
The Manchester United attacker was sidelined late during the Premier League season with a knee injury, but was on the scoresheet in his first appearance since early May.
Rueda was pleased with what he saw from Sanchez, who netted just twice in 27 games for United in 2018-19.
"He's on the right track. We wanted to reserve him for the next games, but he's recovered well," he told a news conference.
Alexis admitted that he has not had it easy in recent months, but was delighted to play a big role for his country.
"For six weeks I felt worse than I ever have before," he said. "I struggled in the first half as I felt stifled but in the second half I was more relaxed and played with more freedom and excitement."
Fellow Chile star Arturo Vidal was also singing the United attacker for his impact after an arduous campaign on the domestic front.
"Alexis needed the goal. He had a difficult year and this gives him confidence," the Barcelona midfielder said of his long-time team-mate .
"We must focus from now on that game. We know that if we keep improving we can be a very dangerous team."
Chile started their title defence in style as Eduardo Vargas netted a brace to go with goals from Erick Pulgar and Sanchez.
Rueda was happy with his team, who moved top of Group C ahead of Uruguay.
"Chile have very experienced players, they know each other very well, with a base of many years," he said.
"The current champions usually make a bad debut, but we worked hard not to suffer with that."