Jonjoe Kenny and Callum Connolly were also named in the starting XI after also being involved in the semi-final, in which England beat Scotland 3-1, but Tom Davies is again on the substitutes' bench.
Roberto Alvarado gave the Mexicans and early lead but Dael Fry cancelled it out later in the half.
Dowell then turned the match on its head nine minutes before the break with a lovely side-foot finish from near the penalty spot.
Superb work on the left from Arsenal winger Eddie Nketiah created the chance for the Everton man to pass the ball inside the post.
Dowell looked to have carved out the goal that could have made the game safe for England when he laid the ball up for Tammy Abraham but the young Chelsea forward somehow put his shot into the post with the goal gaping in front of him.