Guillermo Sebastián Coria (born 13 January 1982), nicknamed El Mago (The Magician in Spanish), is an Argentine former professional tennis player.

Coria achieved his best results on clay, where he won eight of his nine ATP singles titles, and during his prime years in 2003 and 2004 was considered "the world's best clay-court player.

In December 2001, the ATP refused to acquit Coria but reduced his ban from two years to seven months, which meant that he would be free to continue with his tennis career in March 2002.

Coria sued the New Jersey supplements company for more than $10 million in lost prize money and endorsements and settled after the third day of the trial for an undisclosed amount.

Coria went on to win his first Masters Series title at Hamburg by defeating Agustín Calleri in the final in three straight sets.

At the French Open, Coria defeated Andre Agassi in four sets in the quarterfinals, before suffering an upset loss to Martin Verkerk and his booming serves in the semifinals.

In 2004, Coria won the clay-court tournament in Buenos Aires and reached his first Masters final on hard court at the NASDAQ-100 Open, where he faced Andy Roddick.

In attempting to defend his title at the Hamburg Masters, Coria increased his clay-court winning streak to 31 matches by reaching the final, where he lost to world No.

At the French Open, Coria only dropped one set en route to the final, defeating Nikolay Davydenko, Juan Mónaco, Mario Ančić and Nicolas Escudé, before beating former world No.

1, Carlos Moyá, in the quarterfinals and British serve-and-volleyer, Tim Henman, in the semifinals; but he was unexpectedly defeated by unseeded compatriot Gastón Gaudio in an unprecedented all-Argentine final, 6–0, 6–3, 4–6, 1–6, 6–8.

Coria then succumbed to leg cramps for the rest of the match and was barely able to move at times, with many of his serves in the fourth set not even reaching the net.

Coria appeared in five finals after the 2004 French Open defeat and lost four of them, with three of them against the rising king of clay, Rafael Nadal.

Their head-to-head record was deadlocked at 1–1 prior to the match, with Nadal winning their most recent meeting at the Monte-Carlo Masters final weeks ago in four sets.

Eventually, the match went into tiebreak at the five-hour mark, soon after Coria had saved a championship point for Nadal in the 12th game of the fifth set.

Afterward, Coria joked that the small tournament was considered a fifth Grand Slam in his family because his wife Carla hails from Croatia.

Coria had a surprisingly consistent 2005 season, where he was one of only three players to reach the fourth round or better at every Grand Slam, the others being Roger Federer and David Nalbandian.

Despite having a consistent season in 2005, during his tournament victory in Umag he started to suffer from the service yips, a psychological condition that renders a tennis player unable to hit the ball at the correct moment when serving.

Initially, it was not very noticeable, but became more apparent at the US Open, during which Coria served a combined total of 34 double faults in his fourth-round win over Nicolás Massú and his quarterfinal loss to unseeded Robby Ginepri.

Coria's service yips got increasingly worse in 2006, although he still reached the third round of the Australian Open, and even managed a victory over Novak Djokovic at the Miami Masters without serving any double faults.

At the Monte-Carlo Masters, Coria came back from 1–6, 1–5 down to defeat Paul-Henri Mathieu, despite serving 20 double faults in the match.

Coria then defeated Nicolas Kiefer, despite serving 22 double faults, but he was then easily beaten by Rafael Nadal in the quarterfinals.

He lost the first set 3–6 to fellow Argentine Juan Pablo Brzezicki and subsequently retired with a back injury.

In February, in his second ATP Tour appearance of the year, Coria defeated Italian qualifier Francesco Aldi, 6–4, 7–5.

Coria never recovered from the service yips that damaged his game and kept his ranking hundreds of places below his once consistent top-ten position.

[citation needed] As of 2016, Coria has been traveling around Argentina managing the government-funded program "Our Tennis" whose purpose is to promote the sport, and identify and develop talent among children and teens.