In mixed doubles at the 1973 French Open, he and countrywoman Isabel Fernández de Soto lost in the semifinals in three sets to Patrice Dominguez and Betty Stöve.

He became the first Colombian to reach the fourth round of the singles draw at a Grand Slam when he beat three players at the 1976 US Open, Ferdi Taygan, Barry Phillips-Moore and Bill Scanlon.

[1] He remained the only player from his country to go that deep in a Grand Slam tournament until Alejandro Falla made the four round at the 2011 French Open.

He was most notably a member of the side which defeated the United States in the North & Central America Zone final of the 1974 Davis Cup, beating both Harold Solomon and Erik van Dillen in his two singles rubbers.

In the Americas Inter-Zonal final, which curiously featured the South African team, Velasco lost his first match to Bob Hewitt and was defeated in the doubles, to surrender the tie.