A Roddick ace down the
tee on set point sealed the first set after 37 minutes of play.
The South American went up an early break in the second set to post a 2-0 lead before he would then drop the next four games to fall behind 2-4.
Roddick, mixing overpowering forehands and slice backhands to keep del Potro on the run, controlled much of the match as several
errors from del Potro would prove costly.
"He played really well. He served really well," del Potro said.
"I think he played much better than me in the important moments, especially
on the break points. And that was the key."
A 133 miles per hour Roddick serve down the tee forced a del Potro forehand return error on matchpoint to end the one hour and
thirty-four minutes long match.
"This is probably the best match I've played this year including Australia," Roddick said.
"I played one bad game, but besides that. I was making
his holds tough ones. I played pretty good defense. I attacked when I had to. I played pretty smart... mixed up some serve and volley. I didn't
let him get a rhythm. If he sets up for enough balls and gets a rhythm, he can hit it probably harder than anybody. So I was happy with the way
I played today."