netted a forehand and then doublefaulted to trail 3-5.
In the next game on his first setpoint, Federer hit a forehand swinging crosscourt volley wide. Del Potro lost his first breakpoint of the match as he hit a backhand wide after setting it up with an aggressive forehand return. A Del Potro backhand sent long ended set one after 42 minutes.
In set two, Federer broke serve once more to reach 3-2 following another untimely Del Potro doublefault on breakpoint. Del Potro saved two matchpoints before netting a forehand on the third.
For the match Del Potro would doublefault only four times while hitting 12 aces, but the doublefaults would arrive at key moments.
Federer, for his part, kept the ball out of the 6 feet, 5 inches tall Del Potro's power zone by mixing in dropshots and approaching the net. But most potinent today perhaps would be the Federer backhand slice which would change the pace today in many baseline rallies.
The 20 year old Del Potro had earlier in the year won four ATP Tour tournaments, but was no match versus Federer's experience and prowess. Against Del Potro, Federer never lost serve while also maintaining a superior winner to unforced error ratio. Del Potro hit 19 winners to 24 unforced errors while Federer struck 28 winners to 23 unforced errors.
In Saturday's semifinals at Madrid, Spain, Federer, seeded second, takes on the fourth seeded Andy Murray of Britain. Head to head Federer is tied with Murray 2-2 and had lost two matches in a row to Murray before beating him in their last meeting in New York.
In September in the US Open semifinals, Murray snapped world number one Rafael Nadal's grand slam winning streak 6-2, 7-6(7-5), 4-6, 6-4. Nadal of Spain had earlier this year won the French Open and Wimbledon. But in the championship match, Federer defeated Murray 6-2, 7-5, 6-2. The two players have not faced each other since the US Open final.