Key questions for the Australian Open men's semifinals: Sinner vs. Shelton, and Djokovic vs. Zverev

MELBOURNE, Australia — If it seems as if there's always something going on with Novak Djokovic at Grand Slam tournaments, that's because there usually is. Even Djokovic himself acknowledged as much as he prepared to face Alexander Zverev in the Australian Open semifinals Friday after taking painkillers for a hurt left leg.

''I don't recall the last time it was any Slam without some form of drama, to be honest. I guess that's part of it. We are out here competing and giving our best to grab a Grand Slam title,'' said the 37-year-old Djokovic, who needed a medical timeout and got his leg taped while eliminating 21-year-old Carlos Alcaraz in a quarterfinal that felt like a final to the winner.

''A lot of things happen on the way," added Djokovic, who also got involved over the weekend in a dispute with a local TV commentator who insulted him on the air. "That's OK.''

Without saying exactly what's wrong with his leg, Djokovic did say this injury is ''very similar'' to what happened to him at the Australian Open in 2023, when he dealt with a bad left hamstring ... and left with the trophy.

The other men's semifinal is No. 1 Jannik Sinner, a 23-year-old Italian who is the defending champion and unbeaten in his last 19 matches, against No. 21 Ben Shelton, a 22-year-old Floridian in his second major semifinal.

How the rest and recovery Djokovic had planned during the time between his match against Alcaraz, which ended just before 1 a.m. as Tuesday became Wednesday, and his next task will go a long way toward determining which version of him shows up in Rod Laver Arena against the No. 2-seeded Zverev, a 27-year-old German.

''I hope to be able, physically, to be moving freely and to be able to be ready to play five sets,'' Djokovic said as he bids for an 11th championship at Melbourne Park and an unprecedented 25th Grand Slam singles title overall in his first tournament being coached by old rival Andy Murray. ''I don't think I'm going to have, mentally or emotionally, any issue (against) Zverev or to motivate myself or anything like that.''

Here is a look at Friday's matchups:

Whose serve is better, Ben Shelton's or Jannik Sinner's?

Shelton has a powerful lefty serve and loves to flex his biceps in his sleeveless match outfits. He cranked one ace at 144 mph (232 kph) in his quarterfinal win over Lorenzo Sonego on Wednesday, tied for the fastest serve of the tournament.

Also available to Shelton: a high-bouncing kick serve he learned from his father, Bryan, a former tour pro who coaches Ben, and that gives opponents fits.

''It's an unusual serve. And he changes the angles a lot. It's hard to predict and it's heavy off your racket,'' Sonego said. ''So you need to be very decisive when you return, otherwise the ball flies.''

Sinner goes about things a different way. His fastest serve so far was 131 mph (210 kph), but ''he hits his spots with the best of them,'' third-round opponent Marcos Giron said.

During this Australian Open, Sinner has only faced 16 break points and saved 13. He's won 75 of 78 services games, an 96% rate that ranks first among all men who made it past the third round. Shelton is next in that category at 94% (92 of 98).

''It'll be important,'' said Simone Vagnozzi, one of Sinner's two coaches, ''to take advantage of the tiny chances during the match that Shelton allows.''

There is a bigger difference when it comes to returning ability: Sinner has won 29% of his opponents' service games (22 of 75), while Shelton's rate over the past 1 1/2 weeks is 15% (15 of 99).

Does Djokovic's past record matter?

Djokovic certainly owns the better resume than Zverev. Then again, who really can compete with Djokovic in that sort of competition?

This will be Djokovic's 12th Australian Open semifinal (he's 10-1), his 50th at all majors (he's 37-12). Zverev is headed to his third trip to this stage in Melbourne (he's 0-2), his ninth at all majors (he's 2-6).

''If you are in a semifinal of a Grand Slam, you have to expect a tough match," Zverev said. "If somebody's there, that means they have played great tennis. And yes, more often than not, it happens to be Sinner and Alcaraz (or) a Djokovic to get there, because those are the best players in the world.''

What are the betting odds for the Australian Open men's semifinals?

According to BetMGM Sportsbook, Djokovic is a slight money-line favorite in his semifinal, listed at -155 against Zverev (+125), a two-time runner-up at other major tournaments. Sinner, who won the U.S. Open last September shortly after being cleared in a doping case that is still pending appeal, is a much bigger pick against Shelton: Sinner is listed at -1400, Shelton at +750.

What are the head-to-heads for Djokovic-Zverev and Sinner-Shelton?

Djokovic leads Zverev head-to-head 8-4, including 3-0 in Grand Slam matchups. Sinner leads Shelton 4-1, including 1-0 at majors.

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Howard Fendrich has been the AP's tennis writer since 2002. Find his stories here: https://apnews.com/author/howard-fendrich. More AP tennis: https://apnews.com/hub/tennis