Argentine former world number 20 Jose Acasuso, back from an injury plagued 2010 that led to his ranking dropping to 256, upset Alexandr Dolgopolov in the Buenos Aires Open first round on Tuesday.
The Ukrainian seventh seed had come into the tournament, third of four on the Latin American claycourt circuit, in good form having reached the Australian Open quarter-finals and the final of last week's Brazil Open.
Acasuso, playing his first match of the year, never let the 22-year-old settle, breaking serve early in both sets to open leads he never relinquished to win 6-2 6-4.
Top seeded Spaniard Nicolas Almagro, the world number 13 fresh from beating Dolgopolov to lift his second Brazil title on Saturday, cruised through 6-1 6-2 against Argentine qualifier Pablo Galdon.
Home favourite David Nalbandian, the third seed, beat Italian Potito Starace 6-4 6-4, but the match of the day was Stanislas Wawrinka's three-set tussle with Carlos Berlocq.
The 28-year-old Argentine gave the third-seeded Swiss world number 15 a run for his money, making the most of his far greater familiarity with the clay surface before Wawrinka won 6-4 3-6 6-3.
Wawrinka said he did not normally play tournaments in February but opted for Buenos Aires, and Acapulco next week, because Switzerland had no Davis Cup commitment this month.
"This was my first match on clay since the French (Open last year)," Wawrinka told reporters, but added the surface was not his main problem against Berlocq.
"My problem was not the court. He was playing very well, then I improved. It is good preparation for the American clay season," he said.
He will play Indian Wells and Miami in March.
The Swiss, whose game was riddled with unforced errors, battled back from 3-0 down in the first set and then faced an uphill struggle at 5-0 down in the second, saving three set points before losing it.
Regularly struggling with length but delighting the crowd with brilliant backhand shots, he was always on top in the decider but was still pushed hard by his feisty opponent.