Gastón Norberto Gaudio (Spanish pronunciation: [ɡasˈtoŋ ˈɡawðjo];[a] born 9 December 1978) is an Argentine former professional tennis player.

Gaudio's most significant championship came at the 2004 French Open, when he defeated fellow Argentine Guillermo Coria from two sets down in the final.

He lost in Belo Horizonte to Brazilian Francisco Costa, and won in Santa Cruz with a victory over Ecuadorian Luis Morejón, both in August.

Gaudio won two consecutive Challengers in Nice and Espinho defeating Jacobo Díaz and Markus Hipfl, respectively.

2000 saw Gaudio establish himself on the main tour and win his only Challenger of the year in Braunschweig over countryman Franco Squillari, 6–4, 6–7, 6–4.

In addition to his Challenger title, Gaudio made the semifinals in Auckland, Santiago and, in his most impressive performance of the season, the Monte Carlo Masters, where he defeated Marat Safin, Félix Mantilla, Julien Boutter, and Juan Carlos Ferrero without dropping a set, before losing to Slovakia's Dominik Hrbatý in a tough three-set match, 4–6, 7–5, 6–2.

Gaudio soon went back to his winning ways, however, reaching the final of Viña del Mar, losing to bitter rival and countryman Guillermo Coria, 6–4, 5–7, 2–6.

Gaudio would avenge that defeat to Coria in a hard-fought victory in the quarterfinals of Buenos Aires, which involved both players making rude gestures and insulting each other regularly.

In the American hard-court swing after the 2001 Australian Open, he made the quarterfinals of the Miami Masters, losing to 19th seed Jan-Michael Gambill, 6–3, 5–7, 4–6.

Although he did not manage to win his first title in 2001, Gaudio had some success, making a final, a semifinal and four quarterfinals (one of them at the prestigious Miami Masters).

Continuing on from his successful Davis Cup debut, in 2002 Gaudio defeated Ivo Karlović in the fifth match to secure a semifinal place for Argentina.

Gaudio made the fourth round of the French Open, losing to Juan Carlos Ferrero, 7–6, 1–6, 7–6, 2–6, 4–6, while leading 4–1 in the final set.

After Roland Garros, Gaudio made the final in Gstaad and the semifinals in Kitzbühel, losing on both occasions to Àlex Corretja.

After the timeout, Coria, after breaking serve at the change of ends beat his left breast while staring at his opponent, which Gaudio took as an insult.

[5] The other was the Davis Cup in the semifinals against Spain in Málaga, where the two top Argentine players Guillermo Coria and David Nalbandian were unavailable due to injury.

"When I returned to Buenos Aires after playing Davis Cup in Moscow and Málaga, you had the impression it was my fault and that hurt me," he said.

2004 started slowly for Gaudio, but he eventually reached the final in Barcelona, losing to Tommy Robredo in five sets, then posted two victories in the World Team Cup over Martin Verkerk and Lleyton Hewitt.

In fact, the 2004 French Open was the only occasion he progressed past the fourth round of a grand slam tournament.

"[11] He lost in the fourth round of Roland Garros to David Ferrer after leading 4–0 in the fifth set and losing six consecutive games.

Ranked in the top 10, Gaudio started 2006 off well at the French Open, where he lost in the fourth round in four sets to Russia's Nikolay Davydenko.

Later in the month, Gaudio continued his comeback attempt at the Movistar Open in Viña del Mar, Chile.

Granted a wild card into the main draw of the tournament, Gaudio lost to Santiago Ventura, 0–6, 3–6, in the first round.

Gaudio finished the 2008 season unranked[12] as a result of not winning a single match over a period of 12 months, causing his ranking points to fall to 0 by 22 September 2008.

In February 2009, he received a wild card into the main draw for the Buenos Aires tournament, an ATP World Tour 250 event in his home country.

Gaudio was awarded a wild card into the 2009 French Open, where he was beaten by Czech Radek Štěpánek in the first round, 3–6, 4–6, 1–6.

In October, he made the final of the Buenos Aires Challenger, losing to training partner Horacio Zeballos.

[13] In an interview on the Argentine program Vertigo, Gaudio revealed that he had received psychiatric treatment for clinical depression during his time away from tennis.

[14] After a poor start in 2010, he won the San Remo Challenger, defeating countryman Martín Vassallo Argüello, 7–5, 6–0.

He posted an impressive victory over American Lester Cook in the first round but was taken out by Thiago Alves in straight sets in his next match.