Guillermo Vilas (born 17 August 1952) is an Argentine former professional tennis player. Vilas was the No. 1 of the Grand Prix seasons in 1974, 1975 and 1977. He won four Grand Slam titles, the year-end championship, and 62 ATP titles overall. World Tennis, Agence France-Presse and Livre d'or du tennis 1977 (Christian Collin-Bernard Ficot), among other rankings and publications, rated him as world No. 1 in 1977. In the ATP computer rankings, he peaked at No. 2 in April 1975, a position he held for a total of 83 weeks, although some have argued that Vilas should have been ranked No. 1 for at least 10 weeks, particularly in 1977 when he won 2 grand slams. He was inducted into the International Tennis Hall of Fame in 1991, two years after his first retirement.

Vilas is known for his prowess on clay courts. He won more than 650 matches on clay, which is an all-time record. His peak was the 1977 season during which he 16 titles including two majors (both on clay) and had a 53 winning streak on clay which was the longest in the Open Era at his time. In 2016, The Daily Telegraph ranked him as the 3rd best male clay-court player of all time, behind Rafael Nadal and Björn Borg. In 2018, Steve Tignor for Tennis Magazine ranked him as the 16th greatest tennis player of the Open Era.

Historical and statistical studies presented in 2015 by Argentinian journalist Eduardo Puppo and Romanian mathematician Marian Ciulpan concluded that Vilas should have been No. 1 in the old ATP ranking system for seven weeks between 1975 and 1976. The ATP and its chief executive at that time, Chris Kermode, although not refuting the data, decided not to officially recognize Vilas as No. 1. The controversy is still in the legal stage. In October 2020, Netflix released a documentary film about Vilas' case titled Guillermo Vilas: Settling the Score.

Raised in the seaside resort of Mar del Plata, Vilas was a left-hander and played his first tour event in 1968. He was in the year-ending top ten from 1974 through 1982. He was a clay-court specialist and played well on hard-court, grass, and carpet surfaces.

He won four Grand Slam titles: the 1977 French Open and the 1977 US Open (both played on clay) and the 1978 and 1979 Australian Open (both played on grass). He was also the runner-up at the French Open three times (1975, 1978, and 1982) and at the Australian Open once (January 1977).

In 1974, he won the year-end Masters Grand Prix title. In addition, he won seven Grand Prix Super Series titles (1975–80), the precursors to the current Masters 1000.

A left-handed baseliner, Vilas's best year on tour was 1977 when he won two of the four Grand Slam singles tournaments and 16 of the 31 Association of Tennis Professionals tournaments he entered. His playing record for 1977 was 130 wins against 15 losses. Not including the Masters year-end championship, he won 72 of his last 73 ATP matches in 1977. The highest point during this run was winning the last US Open played at Forest Hills against Jimmy Connors 2–6, 6–3, 7–6(7–4), 6–0 in a match where Vilas surprised his American rival by attacking the net. ...

Source: Article "Guillermo Vilas" from Wikipedia in English, licensed under CC-BY-SA 3.0.