A defensive player, he kept improving his return of serve, said by many commentators to be the best in the sport today. He breaks at will, it seems — in the ninth game of a set, for example, so he can serve it out; midway through a tiebreak, to the same effect. Indeed, he closed out the first two sets in the Australia Open with the same serve over the alley on the deuce side. Stefanos Tsitsipas lunged and caught them both, and both times sent them long.