Russia's Dmitry Tursunov stunned David Ferrer 7-5, 3-6, 6-1 on Wednesday to knock the top seed out in the second round of the Barcelona Open.
World number four Ferrer, losing finalist last month in Miami to Andy Murray, was seeded ahead of Rafael Nadal for the first time and had been dreaming of making amends after losing three finals in Barcelona to his career rival.
But the 66th-ranked qualifier Tursunov had his own agenda, which he executed in style in just under two hours to spoil the pre-French Open clay debut of Ferrer.
The seed had missed last week's Monte Carlo Masters, won by Novak Djokovic over Nadal, due to the thigh injury which bothered him during the Miami final.
Ferrer was making his 11th consecutive Barcelona appearance to now stand 25-11 at the venue. The four-time runner-up lost to a veteran also making his first clay start and who last played the tournament five years ago.
Tursunov needed only five aces in a win where he struck 30 winners and 50 unforced errors.
But Ferrer showed his rust with a mere 15 winners and 32 miscues at the Real Club de Tenis.
Tursunov now moves into a third-round encounter with Brazilian 16th seed Thomaz Bellucci.
Nadal was making a start this week in his tilt at an eighth title at his home Catalan venue.
The world number five has won seven of the last eight Barcelona editions and did not play due to injury three years ago.
Canadian fifth seed Milos Raonic made an easy start over Eduardo Roger-Vasselin of French 6-4, 6-2, as the north American made up for a disappointing loss last week in the Monte Carlo second round.
Argentine Juan Monaco crushed Australian number one Bernard Tomic 6-0, 6-2 while Slovak 11th seed Martin Klizan beat Albert Montanes 6-3, 6-4 and veteran Spanish clay campaigner Tommy Robredo continued to find flashes of his best form in a defeat of Bulgarian young gun and 14th seed Grigor Dimitrov 7-5, 6-1.