Del Potro maintains his run

Juan Martin del Potro survived an unexpected struggle with Dudi Sela before edging out the Israeli 6-0 5-7 6-2 in the second round of the Legg Mason Classic on Wednesday to stretch his unbeaten streak to 17 games.

The second seed appeared to be on cruise control as he claimed the first set in 19 minutes after winning 11 of 12 points on his first serve and breaking Sela three times.

Sela regained his composure and won the second set before taking control of the decider.

But world number 19 Del Potro recovered and claimed the win in one hour and 49 minutes.

Del Potro's amazing streak has seen the 19-year-old win three consecutive titles in Stuttgart, Kitzbuhel and Los Angeles, where he beat American world number nine Andy Roddick.

Also on Wednesday, fourth seeded German Tommy Haas overcame an erratic serve to dispatch Frenchman Nicolas Mahut 7-6 (7-4) 6-3.

Haas had 10 of his 12 aces and all seven double-faults in the opening set, but took control late in the match by breaking Mahut twice in the final three games.

Haas will face Colombia's Alejandro Falla, who outlasted Florent Serra 7-6 (7-2) 7-6 (13-11), in the quarter-finals.

Last year's beaten finalist John Isner won the battle of rising Americans after downing Donald Young 6-4 7-6 (7-4) in 77 minutes.

Isner rained down 17 aces and also converted the only break point in the match, which proved the difference in the first set.

2-Juan Martin Del Potro (Argerntina) bt Dudi Sela (Israel) 6-0 5-7 6-2
4-Tommy Haas (Germany) bt Nicolas Mahut (France) 7-6 (7-4) 6-3
Alejandro Falla (Columbia) bt Florent Serra (France) 7-6 (7-2) 7-6 (11-9)
John Isner (USA) bt Donald Young (USA) 6-4 7-6 (7-4)