Del Potro is the first back-to-back Washington winner since Andre Agassi
Defending champion Juan Martin Del Potro claimed a fine victory over top seed Andy Roddick in Washington DC to retain the Legg Mason Classic.
The 20-year-old Argentine fought back after losing the first set to beat the Wimbledon finalist 3-6 7-5 7-6 (8-6).
Consistent serving helped Roddick, playing his first tournament since SW19, to win the first set.
But Del Potro raised his game to take the second, twice breaking Roddick, before winning the final-set tie-break.
"Roddick is in much better condition this year. His game has improved a lot," Del Potro said.
"I beat him, but the difference was so close."
Roddick, back after a hip injury had sidelined him since his Wimbledon final defeat by Roger Federer, added: "I'm not far off from where I was after Wimbledon.
"This is the start of preparation leading up to the US Open. I feel better about my game now than when I got here. The serve will come around with matches."
Both men will continue their preparation for the US Open, which starts on 31 August, at the Rogers Cup in Montreal next week.
Roddick, the 2003 US Open champion, overpowered Del Potro in the early games as he looked to make short work of winning a fourth Washington title.
Serving first, the 26-year-old former world number one cruised through the opening set as Del Potro toiled in the searing heat and struggled to break down his opponents serve often enough to seriously threaten.
However, bidding to become the first back-to-back Washington winner since Andre Agassi in 1999, Del Potro marched back into contention by taking a 5-3 lead in the second set and breaking Roddick in the eighth game.
When world number five Roddick held serve and then hitting back with a vital break to level the set at 5-5, the home favourite looked primed to go on and take the match.
Del Potro, however, found inspiration and broke Roddick's serve before closing out the second set.
As the impact of the hot and humid weather took its toll, both men looked tired in the deciding set.
A horrendous missed smash, which flew off the top of Del Potro's racquet, was followed by a double fault and allowed Roddick to take the vital first break for a 2-1 lead.
But after holding serve to go 3-1 ahead, Roddick was pegged back as Del Potro won three straight games without dropping a point on his own serve to go 4-3 up.
Roddick continued to serve confidently as both men held to crank up the tension and take the match to a deciding tie-break.
In a nervy finale, Del Potro missed out on three championship points before taking the title at the fourth attempt with a cross-court forehand which evaded Roddick and struck the line.