Can Djokovic back up his top ranking?

The post-Wimbledon slumber is almost over for the big three. They're getting ready to compete in Masters 1000 events in Montreal and Cincinnati. Some of the elite women already have been in action, although the stakes are raised at Premier stops in Toronto and Cincinnati.

Here are a few things to watch in the next few weeks, leading off with the dominant men's world No. 1:

Gunning for Djokovic

Pressure? What pressure?

Novak Djokovic looked completely at ease on the "Tonight Show with Jay Leno" on Tuesday. It's clear he can entertain no matter what the venue.

He faces a different type of pressure in Montreal, Cincinnati and, looking ahead, the U.S. Open. Djokovic wasn't the man to beat in Australia, was 50-50 with Rafael Nadal heading into the French Open, and not many picked him at Wimbledon. He's now the substantial favorite during the U.S. Open Series.

Having nabbed the No. 1 ranking, a new, driven Djokovic is determined to maintain his level. He'll lose more than one match this season, although winning in Montreal, Cincinnati and New York isn't a stretch. He's on his best surface.

A worry for Djokovic is the heat. He'll likely be tested in the broiling Ohio conditions. Djokovic had it relatively easy with the heat in Melbourne and London.

Rafa's remedy

Now wouldn't it have been nice to listen in on Nadal's practice sessions with Uncle Toni? Nadal's game has evolved since he turned pro, and he'll have to make more changes to cope with Djokovic, since he's 0-5 versus his buddy in 2011, dropping eight of the past nine sets.

Nadal enjoyed success very early in their Wimbledon final with the forehand down the line but abandoned it as the match wore on. Instead, his favored cross-court forehand to the right-hander's backhand took over, and it didn't work -- again. When Djokovic was stretched on the baseline, Nadal, a fine volleyer, stayed put rather than venturing forward. He's mindful of Djokovic's passing ability, but Djokovic, not as good of a volleyer, wasn't afraid to come in.

The dynamic among the top three is indeed peculiar. Nadal can't beat Djokovic, Djokovic has a tough time with Roger Federer, and Federer wants to avoid Nadal.

Fish's stamina

Players complain about the long season and injuries that result, then enter six tournaments in as many weeks. Strange.

But Mardy Fish did just that, and in a move smelled a mile away, bailed from the Legg Mason Classic in Washington -- as the second seed -- after going deep in Atlanta and Los Angeles. A heel injury was the official reason.

Who'd want to be a tournament organizer, eh? The heel, one suspects, will be fine in Montreal and Cincinnati.

But what about Fish's incongruous results in Canada and Cincinnati? He's played twice in the former, going 0-2, while finishing as the runner-up in Ohio twice, including in 2010. Fish has no points to defend in Montreal but plenty in Cincinnati to back up.

Serena's charge

Even before she hit a ball in Stanford, where she ended up winning the whole thing, Serena Williams meant business. She was in tip-top shape. Losing at Wimbledon to Marion Bartoli stung, although it shouldn't have given her roughly year-long hiatus.

Williams was far more efficient off the ground; the power in her strokes was also accurate, and being in better shape, she covered the court impressively.

The signs are ominous -- for her opponents.

Sharapova's answer

Maria Sharapova had reason to be confident as she embarked on the U.S. Open Series, having reached the semis at Roland Garros and final at Wimbledon. Never one to back down, the Russian said she'd look forward to playing Williams this summer, despite losing five straight to the 13-time Grand Slam winner.

It happened in California, and the streak was extended to six. It was ugly.

Sharapova got crushed in the quarterfinals, a huge blow. For a third time in the past two months, she foundered in a big match. And in those encounters against Li Na at the French Open, Petra Kvitova at Wimbledon and Williams in Stanford, Sharapova tossed in a combined 23 double faults. You almost expect a flurry of double faults now when the world No. 5 confronts top-quality foes.

She needs a morale boost.

The return of Kimmy

Kim Clijsters is back and in her favorite time of the season: Her U.S. Open Series record since 2009 is an impressive 26-3, punctuated by back-to-back crowns in New York.

But will this year be different?

Dissimilar to 2009, when Clijsters re-emerged on the circuit in a story high on feel-good factor, her health is a question mark. Clijsters was already struggling with a shoulder problem prior to two separate foot injuries surfacing, one suffered while the Belgian was at her cousin's wedding.

If Clijsters is 100 percent, even if results don't go her way in Canada, she'll probably be happy enough. She's overcome a lack of matches to win the U.S. Open in the past.