Juan Martin del Potro won his fourth title in as many weeks by beating Viktor Troicki 6-3 6-3 in the final of the $US500,000 ($A575,000) Legg Mason Classic on Sunday.
The second-seeded Argentine continued his superb summer run by winning his 19th-straight match.
He dispatched Troicki in just over 90 minutes, hammering five aces and saving six of seven break point opportunities.
Potro has now won tournaments in Stuttgart, Kitzbuhel, Los Angeles and Washington.
This was his first career meeting against Troicki, who is ranked 93rd and was playing in his first ATP final.
The 19-year-old Potro has won 37 of his last 39 sets during his breakthrough stretch on the tour.
He earned $US80,650 ($A93,000) in first place prize money.