Keys, the No. 19 seed and a two-time semifinalist at Melbourne Park, had won the first set. But Rybakina, who like Keys is a precise winner machine when she is playing the tennis she wants to play, had taken the second by seizing the initiative and playing on her front foot. Halfway to the finish, Keys had become a passive counterpuncher.

The potential championship matchups should bring a lot of intrigue to the first Grand Slam tournament of the year

American tennis player Madison Keys seeks a fourth straight win over a seeded opponent at the Australian Open, when she takes on No. 2 Iga Swiatek in Thursday’s semifinal round.