Madrid, May 11 (IANS): Serbian qualifier Dusan Lajovic rallied from a set down to upset Argentine world No. 6 Juan Martin del Potro 3-6, 6-4, 7-6 (8-6) in third-round action at the Madrid Open and book a place in the quarter-finals of an ATP World Tour Masters 1000 event for the first time.

The victory also was the 95th-ranked Serbian's first-ever win over a top-10 player, reports Efe.

Del Potro squandered numerous opportunities to seal the win over Lajovic, including letting a 4-0 lead slip away in the tie-breaker largely due to unforced errors.

The Serbian grew in confidence throughout the two-hour, 17-minute match against the Argentine, who was playing his first clay-court tournament of the year after a strong early season, hard court campaign that included his first-ever Masters 1000 title (Indian Wells).

Next up for Lajovic will be South African world No. 8 Kevin Anderson, who defeated German Philipp Kohlschreiber 6-3, 7-6 (9-7) in the third round.