At the time, his signing was great business by former tournament director Graham Pearce. He was well outside the top 50 midway through 2008, before a hot streak, when he won his first ATP tournament (in Stuttgart) then added three more in consecutive weeks, a unique feat in the Open era, that launched him into the top 10.
"Auckland was an important tournament for me, it was the first one after the great 2008 that I had, a year in which I won four tournaments in a row, reached the quarters at the US Open and the Davis Cup final," del Potro said. "So I chose Auckland to get off to a good start and have the best preparation for the Australian Open."
At the time, the 1.98m del Potro was a softly spoken giant, still adapting to the constant demands of interviews in his non-native tongue. But he was undeniably charismatic, always prepared to laugh and joke in English.
Del Potro also delivered on court, beating Ernests Gulbis, Viktor Troicki and Robin Soderling (then ranked 17 in the world) before trumping big serving Sam Querrey in the final. "It all went great," he said. "I could recover after losing the first [set] against Gulbis. I won the [next] two matches in straight sets and then [won] the final."
That victory kicked off a remarkable year, where he put Argentine tennis on the map. He beat Nadal and Federer on multiple occasions, reached the semi finals at Roland Garros and the final at the season ending ATP championships in London. But his crowning glory came in New York, when he became the first person to beat both Nadal and Federer at the same grand slam. He trumped the Spaniard in straight sets in the semifinals, then beat the Swiss ace in an unforgettable four hour, five-set final. Federer hadn't lost in New York since 2003 - a 41-match winning streak - with five consecutive US Open titles. It was the only major won by someone outside the big four (Federer, Nadal, Djokovic and Murray) between 2005 and 2013 and cast "Delpo" into a different stratosphere.
"It was a huge change," said del Potro. "Even though I was getting used to being well-known in my country, this was a new experience. I was very young and it was not easy to have all the attention on me. What is important in those situations is to have the right people by your side. You can trust them and they can help you in those kind of situations."
His career has been a wild roller-coaster since - with numerous wrist surgeries and his ranking ballooning above 1000 at one stage - but he has always been defined by his battles with the best.
Besides Djokovic and Nadal, he remains the only other player to beat Federer in a grand slam final and is one of just three active players (Stan Wawrinka and Tomas Berdych are the others) who can claim three wins or more over each of the big four.
"I am honoured to be able to play them and sometimes beat them," del Potro said with a laugh about the famous quartet.
"They push the rest of us to play even better, they made us better players for sure. It's a privilege to play them and those are the matches that I like the most, against the best players in the best tournaments."
Away from tennis, del Potro is a football fanatic, and a high profile supporter of Boca Juniors. He's close to former striker Martin Palermo, and regularly crosses paths with Argentine legend Diego Maradona.
"One of my best friends is Martin Palermo, who was an idol of mine while I was growing up," said del Potro. "[And] Maradona is so supportive of my career - he always has nice words for me. He called me just minutes before one of my wrist surgeries to wish me luck and give me his support. He was also there when we won the Davis Cup in Croatia [in 2016]."
That Davis Cup final cemented his place in Argentine folklore, as he came back from two sets down to defeat Marin Cilic, in front of a hostile crowd in Zagreb.
Despite all the frustrations and time off the court, del Potro can still look back on a storied career, and hopes there is more to come. A decent result in Auckland will see the 29-year-old back in the top 10, before an assault on the Australian Open, which remains the only grand slam where he hasn't reached at least the semifinal stage.
"Of course I wish I could win more big tournaments and climb in the rankings but the main goal for me after all my surgeries is to stay healthy," said del Potro, who returned to the top 20 in September for the first time in more than three years.
"After all that happened to me in the recent years, I am so grateful to be playing on the tour. In 2016, I couldn't play two or three tournaments in a row.
"By the end of 2017, I played five consecutive weeks. So that's a huge improvement."