NEW YORK -- The beating was turning ugly about 10 minutes into the second set of Friday's US Open semifinal between Rafael Nadal and Juan Martin del Potro. Nadal was in a fury, breaking del Potro's spirit, as well as his serve.

The world No. 1 was playing like a man who had a point to prove, and perhaps he did.

Del Potro, who had beaten Nadal the past two times they played, including here in 2009, had morphed into the darling of the tournament.

Rafael Nadal is into his 23rd career Grand Slam final, second-most in history (Roger Federer, 29). Justin Lane/EPA

He had already eliminated No. 3 seed Federer in the quarterfinals earlier this week, leaving Nadal set up to become a punch line in Delpo's developing human-interest story.

Instead, Nadal turned del Potro into a punching bag, advancing to Sunday's final against Kevin Anderson with a fierce win 4-6, 6-0, 6-3, 6-2.

"I was playing so-so at the beginning of the tournament, and I have been playing better and better every day," Nadal said after the 2-hour, 32-minute shellacking. "I wake up today and say to myself, 'Today is the day that I need to play with the right energy, and I need to increase the level of my game.' A lot of times, I know that and it didn't happen. But today it happened. I was playing at the right level to win that match. I'm very happy."

Earlier in the tournament, Nadal had reasons other than the state of his game to be dissatisfied. Although he was top-ranked, he often seemed like a foil for Federer. Would Federer win his third Grand Slam of the year, perhaps beating Nadal for a fourth consecutive time this season in a battle of rivals in renaissance?

But it was the 6-foot-6 del Potro on the other side of the net, a player who wallops the ball every bit as painful as his backstory.

By the start of the third game, that familiar "Ole, Ole, Ole, Del-po, Del-po" chant resounded in Arthur Ashe stadium. Everyone loves Delpo, but Nadal has known comparable frustration, having missed seven Grand Slam events with injury. This year, he has also been emerging from a dreadful slump, playing with replenished intensity and urgency.

However, the urgency that animated the first set was the pace of del Potro's forehand. Nadal followed the playbook in the first 10 games, poking away at the backhand his opponent was trying to hide. But he realized after losing the set that the strategy played right into Delpo's hands.

"I decided to change completely to play much more forehands down the line," Nadal explained. "Then I was more unpredictable, and he was in more trouble, because he didn't know where to go."

The immediate success of the strategy emboldened and unleashed Nadal. Soon his forehands were wicked, dipping shots seeking the lines. His serves were like carefully aimed darts. A famous fussbudget who usually takes all his allotted time between points, Nadal played at a brisk pace, keeping the Argentine titan across the net gasping for air -- and grasping at straws.

The main problem for del Potro is that his wrist surgeries have left him with a compromised backhand that isn't the deadly instrument it once was. It's a solid, reliable shot, but he doesn't have the requisite confidence in it.

"I think it was the first time I was dominated by him," del Potro said. "But it's the first time we played without a good backhand on my side."

Even a Novak Djokovic-grade backhand might not have been enough to stop Nadal on this cool and breezy evening in Queens. A two-time champion at this event, Nadal has known great success, as well as great frustration, on the floor of Arthur Ashe Stadium.

He last won the tournament in 2013, but he hasn't been beyond the fourth round since until this season. Pundits are reluctant to pick him to win because his dominance on clay has often left him vulnerable during the summer hard-court season.

Nadal has one match remaining to prove his point, against a raw-boned ace machine, the 6-foot-9 Anderson. The South African is in his first Grand Slam final. After his win earlier in the day, Anderson climbed into the player guest box to celebrate with his team, a ritual usually reserved for the champion.

The way Nadal is playing, perhaps it was better that Anderson took his shot at the rite. Because Sunday, he could end up looking an awful lot like a beaten-down del Potro.