Rafael Nadal showed his tactical acumen shifting his strategy against Juan Marin del Potro.

Nadal began firing his forehand down the line to open the court then force the 2009 US Open champion to hit his weaker backhand wing on the run during their semifinal match.

Watch: Nadal Roars Into US Open Final

That strategic shift sparked a nine-game run as Nadal rolled past del Potro into his fourth US Open final.

Still, the 15-time Grand Slam champion says the Grand Slam rule prohibiting in-match coaching is "a little bit stupid."

"I know the things that could happen, and I know what I have to do," Nadal said. "Then of course is easy to say. Difficult to make it.

"But I gonna say always the same. Is a little bit stupid that you have a coach traveling for you, with you during the whole season and practicing with you every day, and is a little bit stupid that in the most important moment, he cannot tell you anything.

"In my opinion, will be good if, I don't know if coach have to come on court, but would be good if the coach can talk."

Photo credit: US Open Facebook