Jack Sock did very little wrong in the second set of his first ATP World Tour Masters 1000 semifinal on Saturday afternoon. The American took care of his serve, limited his mistakes and, when he did make them, bounced back with a big serve or forehand to hang around in the BNP Paribas Open’s Final Four.

But he committed the cardinal sin against Roger Federer—he wasn’t perfect.

That alone was enough for the 18-time Grand Slam champion to squeeze through a second-set tiebreak and into the final in Indian Wells, 6-1, 7-6(4), where he will play Stan Wawrinka for his 90th-career singles title.

“He takes advantage so quick,” Sock said after the match. “The room for error is so small.”

Sock was not wrong, and perhaps that is the telltale sign that Federer has returned to—or at least near—his legendary best. For much of the first set, Sock, who was fresh off of the first Top 5 win of his career against Kei Nishikori, looked helpless against Federer.

The 35-year-old, who will find himself at best the No. 6-ranked player in the world on Monday, has looked like he has not left his comfort zone in 2017. Any time his opponents even sniff an opportunity against him, he eliminates it with an unreturnable serve, beam-like backhand, or a prance at the net to put away a volley.

The Swiss seems to be enjoying himself more than ever on and off the court, and winning in every sense of the word. Even his voice is improving.

Back on the court, it is only fitting that a magician came out of Indian Wells’ "Quarter of Death," which initially included Novak Djokovic, Rafael Nadal, Nick Kyrgios, Alexander Zverev and Juan Martin del Potro, among other dangerous players. Not only has Federer avoided death—in the case of a tennis tournament, elimination—but he is seemingly getting better and better with each round.

“Roger is Roger, the greatest player of all time,” Wawrinka, against whom Federer owns a 19-3 record (14-0 on hard courts), said. “He is playing perhaps better than ever.”

A year ago, Federer wasn’t in Indian Wells because he was recovering from a knee injury that ruined his entire season. But this week, he has just one more match left to secure a staggering 90th career title.