Sancho parted ways with the Premier League outfit last summer after a lack of first team opportunities, where his £8m deal to join Dortmund has since reaped its rewards after he successfully broke into the senior set up.
The 18-year-old, who made 12 league appearances last term, impressed during his spell in Chicago as Mario Gotze's converted penalty secured Dortmund an opening victory in the United States.
Sancho admitted he had a particular reason to be motivated against his former club, he said, via Goal: "It was nice to see my old team-mates.
"I'm happy that we won and happy to play against my old club. I had a point to prove and I think I did well in the game. Hopefully, it carries on through the season.
Jadon Sancho is so good. Pace, footwork, sharp movements in half spaces, great passes to break defensive lines. The kid has it all.— usman (@usman_94_) July 21, 2018
"I'm very motivated for the season, very excited. We have a special team."
Dortmund boss Lucien Favre acknowledged the England Under-19 international had "exceptional potential," and the 18-year-old is eager to improve even further and repay his manager's faith next season.
"I'm happy to hear it. I'm glad he has faith in me," he added. "I want to have a great season with goals, assists, and help the team win and carry the team sometimes and I can help the team, that's what I want to do for the season.
"We can reach anything with this squad, that's how great we are when we play as a team and work hard as a team."
Dortmund's pre season tour of America continues with games against Liverpool and Benfica over the next six days.