W2W4: Kerber looks to regain No. 1 ranking, Kyrgios defends title for first time

— -- The busiest month in tennis (17 ATP and WTA events) continues this week with five tournaments and some screaming storylines: Juan Martin del Potro, already a two-time Comeback Player of the Year, returns in Delray Beach;? Angelique Kerber can regain the No. 1 ranking with a win in Dubai; and Nick Kyrgios defends his first title in Marseille against a strong field.

Five of the top-ranked women are scheduled to play in Dubai, while 10 of the top 20 men are set for three events. Here's what else we should be watching for this week:

Dubai Duty Free Tennis Championships, Dubai, United Arab Emirates (outdoor hard)

Top seeds: No. 1 Angelique Kerber, No. 2 Karolina Pliskova, No. 3 Dominika Cibulkova, No. 4 Agnieszka Radwanska, No. 5 Garbine Muguruza

Notable storylines: Against the backdrop of a strong WTA Premier 5 field, Kerber will attempt to wrest the No. 1 ranking back from Serena Williams. A title in Dubai would be enough to give Kerber 21 career weeks at the top, equaling Tracy Austin and Maria Sharapova. Williams isn't scheduled to play again until the event at Indian Wells in March.

In the eight years of Premier 5 and premier events, no one has won more of those matches than Radwanska (163). Serena (13) has won the most titles. Pliskova, the winner last week in Doha, will try to equal Martina Hingis and Justine Henin as the only Doha-Dubai double winners since 2001.

Of note: Eugenie Bouchard (abdominal), Svetlana Kuznetsova (abdominal) and Sara Errani (defending champion/adductor) are all out. CiCi Bellis, a 17-year-old American, is in the draw -- her first WTA-level event of the year.

Hungarian Ladies Open, Budapest, Hungary (indoor hard)

Top seeds: No. 1 Timea Babos, No. 2 Lucie Safarova, No. 3 Julia Goerges, No. 4 Sorana Cirstea

Notable storylines: This first-time tournament is marked by this fun fact: The top two singles seeds, Babos and Safarova, are scheduled to play doubles together.

Of note: Andrea Petkovic and Maria Sakkari (foot injury) will not play.

Delray Beach Open, Delray Beach, Florida (outdoor hard)

Top seeds: No. 1 Milos Raonic, No. 2 Ivo Karlovic, No. 3 Jack Sock, No. 4 Juan Martin del Potro, No. 5 Sam Querrey (defending champion)

Notable storylines: North America's first outdoor tournament of the season could feature some epic collisions. Del Potro, who missed five Grand Slams with a wrist injury, made a dramatic debut here a year ago ranked No. 1,042. He eventually reached the third round at Wimbledon and followed it up with a quarterfinal run at the US Open. After playing in the Davis Cup final (and winning), he wasn't ready to compete this year in Melbourne. He's not quite sure what to expect.

"I don't know yet," the 28-year-old Argentine told ATPWorldTour.com. "I am in my first tournament and the sensations are different than the last match of the year. Always Delray is a good tournament to start."

Except that his first-round opponent is a tricky one in Kevin Anderson, the 2012 winner and a 2014 finalist. The No. 1-seeded Raonic makes his tournament debut, and top Americans Sock, Querrey and Johnson are also in action.

Of note: Tommy Haas, the 38-year-old German and 2006 Delray champion, is playing on a protected ranking and plans to retire after the season. In a few weeks, he'll really get to work as the tournament director at Indian Wells.

Rio Open, Rio de Janeiro, Brazil (clay)

Top seeds: No. 1 Kei Nishikori, No. 2 Dominic Thiem, No. 3 Pablo Cuevas (defending champion), No. 4 Pablo Carreno Busta, No. 5 Albert Ramos Vinolas, No. 6 David Ferrer

Notable storylines: The season's fourth ATP 500-level event is already underway at the Jockey Club Brasileiro, which features eight clay courts. Nishikori, a finalist Sunday in Buenos Aires, is scheduled to make his Rio debut. Previously, Nishikori was the runner-up in Brisbane and lost in five sets to Roger Federer in the fourth round of the Australian Open. The 34-year-old Ferrer, who is 10-2 in Rio, finished outside the top 20 last season and failed to reach an ATP final for the first time since 2004.

Of note: Jamie Murray and Bruno Soares, last year's No. 1-ranked doubles team, are in action but could be pushed by No. 2 seed Lukasz Kubot and Marcelo Melo and No. 3 Carreno Busta and Cuevas.

Open 13 Provence, Marseille, France (indoor hard)

Top seeds: No. 1 Gael Monfils, No. 2 Jo-Wilfried Tsonga, No. 3 Nick Kyrgios (defending champion), No. 4 Lucas Pouille

Notable storylines: A year ago, Kyrgios defeated Richard Gasquet, Tomas Berdych and Marin Cilic -- all in straight sets -- to win his first ATP World Tour title. The 21-year-old Aussie also won titles in Atlanta and Tokyo in 2016?to finish a career-best No. 13 at year's end. He has played only three matches in 2017, one in Davis Cup and two in Melbourne, where he lost to Andreas Seppi in the second round.

No. 1 seed Monfils, the 30-year-old Frenchman, is coming off a fourth-round loss at the Australian Open against Rafael Nadal. The No. 2-seeded Tsonga was a winner this past week in Rotterdam.

Of note:? Alexander Zverev, the 19-year-old German who won the title a week ago in Montpellier, is one to watch. Tsonga and No. 7 seed Gilles Simon are also former winners here.