Sometimes, it’s a gift, while in other instances, you have to earn it.

Whatever the circumstance, the wildcard, which grants direct entry into a tournament, can be a true difference maker, sometimes at a history-defining level. Novak Djokovic was unable to make the most of his at the ATP Tour stop in Acapulco, but here are some players that used it to their advantage.

1

In one of the biggest surprises in the game’s history, three-time Wimbledon finalist Ivanisevic won the title over Patrick Rafter. It was a desperate grab at the title as injury and a loss of form had put a major dent in the big-serving Croat’s ranking.

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2

After two years away from the sport, a time in which she also became a mother for the first time, Clijsters launched a comeback in the summer of 2009. She made the most of her wildcard at the US Open, winning it over Caroline Wozniacki.

3

Williams won the title at the BNP Paribas Open in 2001. It would be more than a decade before she stepped foot on the tournament grounds again after an infamous boycott. The world No. 1 announced she would return in 2015, and while she didn’t win again, it made for one of the biggest moments in tennis that year.

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4

Like Clijsters, fellow Belgian Henin also decided to make a comeback from an early retirement. She found success in her first WTA tournament back, making the final in Brisbane. Henin made her biggest ripple less than a month into the season by making the final of the Australian Open as an unranked player. Unlike Clijsters, she didn’t capture the title, but a runner-up finish in a major isn't too shabby.

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5

And thus, a Hall of Fame career is born. Hewitt won the title as a 16-year-old wildcard, becoming the third-youngest ATP titlist in history, in his hometown tournament. He beat fellow Aussie Jason Stoltenberg in the final, but it was his win over Andre Agassi in the semis that really announced him on the world stage.

6

In a field that included Grand Slam doubles champions and finalists at every twist and turn, it was the unseeded wildcard pairing of Marray and Nielsen that came away with the 2012 Wimbledon title. Marray ended a 76-year British drought in men’s doubles. Nielsen, of Denmark, was familiar with All England Club success by way of genetics: His grandfather played two singles finals there in the 1950s.

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7

Probably the best word to describe Istomin’s career would be “solid.” Prior to the start of 2017, he’d won a singles title and cracked the Top 35 at one point. He had to earn a wildcard into the Australian Open this year by way of winning a tournament just to get there. Istomin then won his first-round match, but was expected to be a mere bump in the road for six-time champ Novak Djokovic.  Instead, Istomin obviously missed that memo as he caused the upset of the tournament.

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8

Who knows what the landscape of men’s tennis would look like today if Del Potro had been fully healthy for the past few years? Last year was another comeback year for him from a wrist injury, as he really found his form at the Rio Olympics (winning silver). In his last tournament before the Davis Cup final (which he helped Argentina win), the 28-year-old cemented his return with a title in Stockholm as a wildcard entrant.