Road to the US Open: Djokovic, Serena, Halep among top storylines

Will Djokovic set the new mark for most Grand Slams all time? (1:19)

John and Patrick McEnroe discuss Novak Djokovic's place among the best to play the game and examine his chances of finishing with the most majors. (1:19)

The ATP and WTA pros have rounded the final turn and are entering the homestretch of the Grand Slam season, with the US Open looming at the finish line. There's still a ways to go, though -- the robust (12-event) hard-court season began this week in Atlanta.

This segment can be grueling, given the punishing hard surface and sometimes blazing-hot weather, factors that are sometimes exacerbated by the fatigue some players feel as the end of summer approaches. But at the moment, all the big names except for Novak Djokovic and Roger Federer are entered in the two main events of the segment: the Rogers Cup (aka Canadian Open) and the Cincinnati combined event. (Djokovic had been entered in both but withdrew from the Rogers Cup on Thursday, citing rest and recovery.)

Here are some of the key storylines and questions we have as tennis returns to North America.

Can Naomi Osaka regroup?

It's almost surreal to think that shortly before the French Open began, Osaka -- the winner at the most recent US and Australian Opens -- told the Times of London: "Of course for me I would love to have the career Grand Slam. It would be even better to make it a calendar [year Slam -- something not even Serena Williams has achieved]. That's definitely my goal."

Those dreams of joining the three women who have completed calendar-year Grand Slams are now dead as year-old tennis balls. Osaka went 2-2 at the French Open and Wimbledon. She hasn't won a title since she stoked dreams that she might inherit Williams' mantle by winning her second consecutive major at age 21 at the Australian Open. Jermaine Jenkins, her coach since the end of February, hasn't been able to jump-start that potent, aggressive game. Osaka is 14-10 since winning in Melbourne. She cut short her news conference after her first-round loss to Yulia Putintseva at Wimbledon, asking the moderator: "Can I leave [the room]? I feel like I'm about to cry."

There may be light at the end of the tunnel. Osaka is at her best on hard courts, as her two-year 44-18 record and two Grand Slam titles suggest. (By contrast, she is 7-5 on grass and 14-6 on clay, with nothing better than a semifinal on each.) She's had time to firm up a relationship with Jenkins. She will feel comfortable in North America: Born in Japan, she has lived in the U.S. since she was 3.

Osaka is a self-professed "overthinker" who said at Wimbledon that she experienced "way more" stress and pressure than she anticipated after she hit No. 1 in the rankings. That kind of honesty and self-knowledge will help her. She has plenty of time to dial in her A-game again.

Can Novak Djokovic be stopped?

Top-ranked Djokovic leads the ATP field heading into August. There's a real chance that by the time the final major of the year rolls around, the defending US Open champion will be as close to a prohibitive favorite as, say, Nadal has been at Roland Garros.

The summer hard-court events are a mirror image of the back-to-back early-season Masters 1000 meetings at Indian Wells and Miami. Djokovic notably stumbled at those events, losing in the second round at the former and one round later in Florida. But there's one enormous difference in that mirror image: Indian Wells and Miami take place after a Grand Slam (the Australian Open), while the upcoming ones precede one. File that under "motivation."

Djokovic, who won't play in Canada this year, has taken a total of five titles in Canada (4) and Cincinnati (1). Nadal also has five, with four in Canada. Federer, though, puts them both in the shade with nine total (seven in Cincinnati).

The problem for Federer is unavoidable. He's fast closing on his 38th birthday, which is one reason he's decided (once again) to skip Canada. He'll have a lot riding on his appearance in Cincinnati.

Nadal is the defending champion in Canada, but that's been his only win at either event since 2013. So what? He went on last year to play arguably the best men's match at the US Open -- his five-set quarterfinal win over Dominic Thiem. Knee problems then forced Nadal to retire during his semifinal with Juan Martin del Potro. That makes it easy to overlook just how dangerous Nadal still is in Flushing. Nadal took a disappointing loss to Federer at Wimbledon, but his tender knees held up well.

Where will Serena Williams appear?

If you look at the WTA website or any of the other sites that publish player schedules, you'll see that Williams is entered in both big hard-court events. That's deceptive, though, because on both tours the players who are eligible by ranking for entry in mandatory events are automatically entered until they declare themselves out.

After Williams was upset in the third round of the French Open, she hinted that she might play at least one tune-up event before Wimbledon. She never did. After losing to Simona Halep at Wimbledon, she speculated: "Maybe playing other finals outside of Grand Slams would be really helpful, just to kind of get in the groove, so by the time I get to a Grand Slam final I'm kind of used to what to do and how to play."

Williams acknowledged she is entered in Toronto and Cincinnati but also expressed concern about the impact extended play would have on her own compromised knee: "I think if I overdo it, then that could also be a problem as well. Especially on the hard courts. I've been on the softer surfaces, so to say. It would be interesting to see how my knee is on the hard court."

Williams does not always play in the Canadian Open. She is a Cincy regular, though, appearing uninterrupted from 2011 through 2015 and also last year when she lost to No. 8 seed Petra Kvitova in her first match.

Beware Simo

Who would have predicted at the start of Wimbledon that Halep would not only reach the final but end up playing the most flawless of finals -- against Williams, no less -- since tennis stats have been kept? If there's a lesson in that, it's surely this: Don't underestimate Simo's chances anywhere, anytime.

Halep had said a few times earlier this year that due to her Grand Slam breakthrough at the French Open last year, she was feeling "chill" about 2019. Some took it as code for indifference, and not without reason: Halep's ranking slipped from No. 1 in early February to No. 7 by the time the tour left clay. She played just two finals this year before Wimbledon, losing to No. 21-ranked Elise Mertens in Doha and Kiki Bertens in Madrid. Halep got just seven games off, then faced defending Wimbledon champion Angelique Kerber when they met in the third round of Halep's only grass-court tune-up, Eastbourne.

But Halep showed at Wimbledon what a resourceful, bold, gritty player she can be when she's feeling "chill." If the word is code for anything, it's for her self-proclaimed victory over a career-long battle with negativity. As she said at Wimbledon: "I was too negative. I could not see the things I was doing great."

If she can sustain the confident attitude and lightheartedness that powered her drive to the Wimbledon title, she could end up with a career Grand Slam. She's already locked in the most extreme surfaces (clay and grass) and has just the two hard-court slams to go. She lost a very close final Down Under in 2018 and has been a US Open semifinalist. Halep has won on the hard courts at Indian Wells, and she's 2-4 in finals at the two big summer hard-court events.

Expect the unexpected

A number of relatively unknown players have suddenly gotten very good either overnight or, in some cases, over the long haul. Take Roberto Bautista Agut, the 31-year-old Spaniard who's become one of the toughest outs in tennis. As Djokovic said after he halted a two-match skid against Bautista Agut in the Wimbledon semifinals: "Mentally he's very consistent. He stays there. He's very focused. You will not see any outbursts or any downs, so to say, in his attitude on the court. I respect him a lot."

Matteo Berrettini has caught fire, both on clay and grass. That means he ought to be fine on hard courts too. A 23-year-old Italian, Berrettini has shot up out of nowhere to establish himself in the top 20 with a 23-5 record from mid-April through Wimbledon. Berrettini's countryman Fabio Fognini is a magician with a racket. While he excels on clay, his game adapts well to hard court. He's just one step short of his career-high No. 9 ranking.

Ugo Humbert, a 21-year-old southpaw from France, did better than any of his next-gen peers at Wimbledon (he made the quarters). A pair of next-gen buddies and Canadian natives, Felix Auger-Aliassime and Denis Shapovalov, are likely to get fired up in Montreal. Shapovalov has been struggling; F2A has passed him in the rankings and, at No. 23, is just two places behind the youthful godfather of the Canadian breakout, Milos Raonic. Don't forget his name either in the coming weeks.

The women have specialized in the unexpected lately, with Ashleigh Barty zooming to the No. 1 ranking as swiftly as Osaka has fallen. Barty will likely figure prominently for the first time during the long hot summer. Elina Svitolina is on the upswing again, as are Johanna Konta and Anett Kontaveit. Victoria Azarenka and Garbine Muguruza may be household names, but they're easily overlooked. That could be imprudent.