Japan's Kei Nishikori continued his march upwards the rankings with a first round win at the Copa Claro ATP event on Monday.

Nishikori beat former world no. 1 Juan Carlos Ferrero 7-5, 3-6, 6-2 in Buenos Aires.

"It was a tough match," commented Nishikori. "Ferrero is a very good clay-court player. I was a little nervous but started to feel more confident and playing better. I like to play here."

Sixth seed Stanislas Wawrinka beat Horacio Zeballos 6-3, 6-4 while Carlos Berlocq beat Pere Riba 6-7(5), 6-0, 6-0.

Fernando Gonzalez  was leading Albert Montanes 7-5, 1-0 when the Spaniard retired with a back injury.

Gonzalez is scheduled to retire after next month's Miami Masters