US Open 2021: The mind-boggling numbers behind Novak Djokovic's pursuit of a Grand Slam

Zverev outlasts Djokovic in epic 53-shot rally (1:21)

Alexander Zverev beats Novak Djokovic to win the longest rally of this year's US Open. (1:21)

NEW YORK -- When Novak Djokovic takes the court at Arthur Ashe Stadium on Sunday, he will attempt to do something only three other tennis players have accomplished in the history of the sport: win a calendar-year Grand Slam.

The world No. 1 has had a perfect Grand Slam year, winning all 27 matches he has played and lifting three major trophies.

He is one match -- and three sets -- away from making history two times over: becoming the fourth player to win the calendar-year Slam and also surpassing Roger Federer and Rafael Nadal for a record 21 major titles.

"I'm going to treat this match as [if] it is my last one because it's arguably the most important one of my career, maybe," Djokovic said after Friday's semifinal battle against Alexander Zverev.

One could argue that he's treated every Grand Slam match this year like it's the most important one of his career, considering his perfect record.

Ahead of Sunday's match against Daniil Medvedev (4 p.m. ET; ESPN/ESPN App), here's a look at some of the mind-boggling numbers Djokovic has put up on the tennis court this season. All numbers are through Friday's semifinal.

49.61: Number of miles Djokovic has run at the four majors combined

Djokovic has played 27 matches at majors this year (and won all of them), and he has run a total of 49.61 miles in those 27 matches. It's a little less than the distance of two full marathons (a marathon is 26.2 miles long).

53: Number of shots in Djokovic's longest rally

In the semifinals of the US Open, Djokovic and Zverev were involved in a 53-shot rally in the third set, which Djokovic led 5-4 (with one set apiece). In the most pivotal point of the match at 40-30, up a break and with set point in sight, Djokovic decided to give his everything, hitting baseline forehand shots with precision. Djokovic rarely grunts during points, yet after 25 shots, the world No. 1 began grunting with every return. That was when fans realized how long the rally had been. Zverev held on to win the point, forcing a deuce with a massive forehand winner.

"He plays the best tennis when he needs to, which a lot of players don't. That's why he's the world No. 1," Zverev said at the news conference following the match. "He comes up with the best tennis when he needs to. We play [53]-shot rallies. The only way for me to win that rally is to hit a forehand winner. That says it all, on a set point."

11 minutes and 15 seconds: Duration of longest game played

In June this year, Djokovic did something that's since been talked about as one of the best moments of his career: He beat Rafael Nadal, the King of Clay, in Roland Garros. The match, which lasted 4 hours and 11 minutes, felt like the final of the tournament. After the third-set tie breaker, the French government, which had imposed an 11 p.m. curfew due to the pandemic, gave an extension for the 5,000 people in the stadium so they could continue watching the duel. Djokovic won the match 3-6, 6-3, 7-6, 6-2, against a man whose Roland Garros record is 105-2.

"It is surely the greatest match I have played here in Paris," Djokovic said after the match.

4,954: Total number of forehands hit

5,107: Total number of backhands hit

3,796: Total number of serves hit

130: Fastest first serve this year (in miles per hour)

37: Percentage of first serves unreturned

4: Number of five-setters played in a Grand Slam

The first five-setter came against the American Taylor Fritz in the third round of the Australian Open. He held on 7-6, 6-4, 3-6, 4-6, 6-2. Drama ensued throughout the match. First, the match was paused during the fourth set to ensure the spectators left because of a COVID-19 lockdown rule in Melbourne. Second, Djokovic said he tore an abdominal muscle after a slide during a point. He said he wasn't sure if he would recover in time for the next match. But he did, and he ended up winning the tournament.

The second one was against Italy's Lorenzo Musetti, in the fourth round of the French Open. He shockingly lost the first two sets and had to dig himself out of a hole before Musetti retired at 4-0 in the fifth set. The final score read 6-7 (7), 6-7 (2), 6-1, 6-0, 4-0.

The third one also came in the French Open, in the final against Stefanos Tsitsipas. Again, he came back from being two sets down to lift his second ever Roland Garros trophy 6-7 (6), 2-6, 6-3, 6-2, 6-4.

And the last one happened this week in the semifinals of the US Open against Zverev. After losing the first set like he has for most of the matches this tournament, Djokovic's focus slipped in the fourth set, which Zverev capitalized on, forcing a fifth. Djokovic raised his game in the fifth set to beat Zverev comfortably, 4-6, 6-2, 6-4, 4-6, 6-2.

"There is a reason why he's won 20 Grand Slams. There's a reason why he's spent the most weeks at world No. 1. There's a lot of reasons for that," Zverev said after the loss. "I think mentally he's the best player to ever play the game. Mentally in the most important moments I would rather play against anybody else but him."

81-19: Total number of sets won vs. lost in Grand Slams in 2021

Apart from the four five-setters in which he lost eight sets, Djokovic has played 11 four-setters in Grand Slams this year, while he has won 12 matches in straight sets.

337: Number of ongoing weeks as world No. 1

In March 2021, Djokovic surpassed Federer's nine-year record for weeks spent as the world No. 1. Federer broke 286 weeks at No. 1 on July 16, 2012.

Data credit: Hawk-Eye Innovations.