NEW YORK—Beating the players you're supposed to: It's something we expect from every pro, but particularly those in the Top 20, the elite caste commonly playing on show courts and seen on television.

Janko Tipsarevic, the newest member of the ATP Top 20—thanks in large part to his semifinal run in Montreal—was away from the spotlight today, trading blows on Court 11 with Philipp Petzschner. The setting should have been familiar to the Serb, himself a commoner not long ago, much like his irritable German opponent. Neither man dissapointed today: Petzschner threatened to thrash his racquet against the back wall, yelled into a towel multiple times, and at one point tried to take a bite out of his strings. As for Tipsarevic, he beat a player he was supposed to for the second consecutive round, winning in four sets, 6-0, 6-3, 3-6, 6-3.

One of the biggest reasons for Tipsarevic's ascendance is his serve; he's fine during rallies but has been earning more free points with just one swing. During warm-ups, Tipsarevic's command of the stroke was evident—he seemed to put the ball anywhere he wanted, at any speed. During the match, the Serb was broken just once (compared to five for Petzschner) and that edge gave Tipsarevic another advantage: Petzschner went for too much. Exuding confidence, Tipsarevic passed and lobbed his aggressive adversary enough times to blank him in the opening set, and 60 minutes in, he was leading by two sets.

But there were also ocassions in which Petzschner didn't go for enough. He can fall in love with his slice backhand, but a better example is the 30-all point in the fourth set, a juncture when Petzschner was threatening to make a real match of this. The point before, Petzschner had struck a lovely volley winner, but this time he let a floating ball go—and a millisecond later, it dropped inside the baseline. It was around this time that Petzschner called for a towel just to scream into it.

A point later and Tipsarevic had the break, and Petzschner was unable to break back. Three days after he ousted a qualifier in straight sets, Tipsarevic quashed a comeback bid, setting up a third-rounder with Tomas Berdych. It's not a player Tipsarevic is supposed to beat, but the way he's been playing this season, that may not matter.

—Ed McGrogan