Del Potro and Delbonis did their best to win second-serve points. (AP Photo)

Juan Martin del Potro was exalted for his role in Team Argentina laying claim to the 2016 Davis Cup, though Federico Delbonis ultimately clinched the championship tie for his country in a straight-sets rout over Ivo Karlovic.

Still, Delpo's two-sets-down comeback against Marin Cilic in the other final-day singles rubber will go down as one of the most courageous performances in a Davis Cup final. Of maximum importance in such tense situations: the serve, a shot controlled entirely by the one striking it. It's an original creation each time, not a reactive adjustment.

A new look at serving-percentage trends from the ATP World Tour indicates that it's the second serve that has become crucial for the sport's players, and the one of two opportunities each time they step up to the baseline to serve that might make the difference in a tight match. The ATP considers "excelling" on serve to be winning 80 percent of first-serve points and/or 55 percent of second-serve points.

ATP players peaked on the first-serve stat in 1996, when eight of them (including Goran Ivanisevic, Pete Sampras and Boris Becker) won more than 80 percent of first-serve points. It's in 2011 that ATP stars did their best in winning second-serve points, with 11 taking 55 percent or better, including, interestingly, both del Potro and Delbonis, among some titans of the sport whose names you'll recognize.

What's interesting about the ATP's data is that the number of first-serve percentages topping 80 for its players has notably tapered off, while pros in men's tennis are seeing increased success in recent years in keeping their second-serve points-won percentages above 55.

The lesson here is for both men's and women's tennis, and for club-level players: A player—be it Milos Raonic, Karlovic, Serena Williams, Karolina Pliskova or a local-league player—can have a huge first serve, but he or she best be able to back it up with a strong second serve.

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