NEW YORK (Reuters) – A year ago, few would have bet Roger Federer and Rafa Nadal would be the top contenders at the 2017 U.S. Open, yet the Swiss maestro and the Spanish juggernaut start their campaign with the favorites tag on Tuesday.

Federer and world number one Nadal won the first three grand slam titles of the season as they came back to prominence with a bang, and nothing suggests their first-round opponents, American Frances Tiafoe and Serbian Dusan Lajovic, will bother them.

Federer closes proceedings on center court, which was equipped with a roof last year that could prove helpful as rain might disrupt the action at Flushing Meadows.

Women’s world number one Karolina Pliskova of the Czech Republic will get things going on Arthur Ashe against Poland’s Magda Linette before defending champion Angelique Kerber takes on talented Japanese Naomi Osaka.

Canadian Eugenie Bouchard, who is suing the U.S. Tennis Association for negligence after she sustained a concussion in a fall on the locker room’s floor in New York last year, takes on Russian Evgeniya Rodina on Grandstand.

Former champion Juan Martin Del Potro, the 24th seed, is also in action, against Swiss Henri Laaksonen.