Here are some milestones to watch for in 2019 (and some could happen as early as January).

Follow the second day of the 2019 Laver Cup, throughout Saturday, here. After the first day of play, Team Europe—the only champions the three-year-old event has ever known—led Team World 3-1.

What’s more, each of Roger Federer, Rafael Nadal and Novak Djokovic all have their own unique traits that make them stand out ...