In 1996 he won his first Challenger event in Birmingham, Alabama over Bill Behrens 6–4, 6–4 and his quarter final performance in Bournemouth was his best showing on the main tour.

Later in the year Zabaleta made his first semifinal in Amsterdam losing to Magnus Norman and then in November he won his first ATP title as a senior at Bogotá defeating Ramón Delgado 6–4, 6–4 in the final.

Zabaleta reached the third round of the 2000 Australian Open his best ever showing at the event before losing to Andre Agassi, but he was involved in an Americas Zone Group Davis Cup tie with rivals Chile in Santiago when Zabaleta was leading 7–5, 2–6, 7–6(1) 3–1, when sections of the Chilean crowd incensed by what was perceived to be bad calls against Nicolás Massú threw missiles, fruits, coins, bottles, plastic chairs among other things.

While there were no titles in 2001 and 2002 for Zabaleta, he achieved his best ever Grand Slam performance surprisingly at the US Open where he made the quarter-finals on a fast hardcourt, whereas most of success has come on the clay.

He defeated Sébastien Grosjean who was in the top 10 at the time, in the first round, then Taylor Dent, Greg Rusedski and Xavier Malisse were beaten before Marat Safin ended his run.

He made the semi-finals of the Italian Open defeating Tim Henman and Nicolás Massú who were both in the top 15 at the time, before losing to Carlos Moyà.

In the third round of the Monte Carlo Masters, Zabaleta was leading David Ferrer by a set and had to be carried off the court with a foot injury which kept him out for two months and he missed the French Open in the process.

He came back to play in Båstad and lost in the quarter-finals to Tomáš Berdych and made the semi-finals in Kitzbühel and after a series of poor results, then he had surgery on his knee.

After playing on the Challenger circuit in 2009, Zabaleta retired from tennis in 2010 and is now taking part on a TV show on ESPN[1] Archived 2010-04-06 at the Wayback Machine In 2004 he started his own show called Tenis Pro in which he takes the video camera with him to all the tournaments and highlights life on tour in a light hearted manner and along with Juan Ignacio Chela conduct various interviews with other players, along with other various skits.