NEW YORK (AP) — A decade or so ago, Serena and Venus Williams ruled tennis together, swapping the No. 1 ranking and meeting in Grand Slam final after Grand Slam final.

Serena, the younger of the two, still holds a spot at the top of the game. Venus has not been there for quite some time.

So there was a turn-back-the-clock feel to Day 1 at the 2013 U.S. Open, when both sisters were about as good as can be, dropping a combined four games in Arthur Ashe Stadium. Venus, now ranked 60th, beat 12th-seeded Kirsten Flipkens 6-1, 6-2 Monday afternoon, and then Serena reduced 2010 French Open champion Francesca Schiavone to seeking comfort from a ball boy’s hug during a 6-0, 6-1 runaway under the lights at night.

In the last match of the night session, 17- time major champion Roger Federer vs. 62ndranked Grega Zemlja of Slovenia, was postponed until Tuesday.

Others in action today include the top-seeded man, Novak Djokovic, and two-time Australian Open champion Victoria Azarenka.

Also on Monday, Alisa Kleybanova of Russia won her first Grand Slam match since being treated for cancer, beating 44th-ranked Monica Puig of Puerto Rico 6-4, 3-6, 7-5 on Monday at the U.S. Open.

The 24-year-old Kleybanova was ranked as high as 20th, but after missing much of the last two seasons because of her illness is now 363rd.