Ukrainian seventh seed Alexandr Dolgopolov was bundled out of the Argentina Open by Diego Schwartzman in three sets on Monday.
Dolgopolov came unstuck against the unseeded Argentinian, who rallied to win 5-7 6-4 6-3 on the clay courts in Buenos Aires.
Schwartzman, who was stretchered off the court after collapsing and suffering a full-body cramp at last month's Australian Open, looked destined for an early exit in the capital as Dolgopolov took out the first set.
But Schwartzman powered back to see off the 2011 Australian Open quarter-finalist in just over two hours at the ATP 250 tournament.
Former champion Nicolas Almagro had no such trouble as he advanced to the second round via a straight-sets win against fellow Spaniard Albert Montanes.
Almagro, who won the event in 2011, defeated his countryman and qualifier 6-3 6-3 in his first match since losing in the second round of last month's grand slam in Melbourne.
The 30-year-old hit 11 aces and fended off all four break points.
Elsewhere, Santiago Giraldo defeated Ingo Cervantes 6-1 7-5 and Leonardo Mayer overcame Guido Pella 2-6 6-3 6-3 in an all-Argentinian affair.