In a match filled with frayed nerves and broken serves, the second-seeded Azarenka won despite committing 25 unforced errors with only 15 winners. There were only five holds of serve over the 18 games, but Azarenka had four of them.
ACE™ Brand Pressure Point of the Match: Like Stanislas Wawrinka in his quarterfinal with Andy Murray, Azarenka needed six set points to close out the first set, which swung back and forth. Vika finally put an end to it with a strong serve up the T; Pennetta barely got her racquet on the ball.
When she held for the final time, finally closing out the 83rd-ranked Pennetta on the third match point, Azarenka let out the last of the afternoon's many shrieks to celebrate making her fourth Grand Slam final.
"It was a little bit tricky," Azarenka said. "I couldn't find my rhythm at the beginning. I felt I was rushing too much. I couldn't really put the ball in play. It's good I stayed tough, played well in the return game at important moments."
Azarenka will play the winner of Friday's later semifinal between defending champion Serena Williams and Li Na. A Williams-Azarenka final would be a rematch of last year's high-quality, three-set win for Williams.
Azarenka, the Australian Open champion in 2012 and 2013, improved to a tour-best 31-1 on hard courts this year. She is trying to become the first person to win the Australian and U.S. Opens in the same year since Martina Hingis in 1997.
But Azarenka, who served six double-faults and screamed out in frustration after dumping a pair of easy volleys into the net in the first set, would almost certainly need to bring her game up a couple levels if she wants to win her first U.S. Open title.
Typical of this match was a sequence after Pennetta had broken Azarenka to pull within 4-2 in the second set. Azarenka hit a looping drop shot that Pennetta reached in plenty of time -- but the Italian, in her first Grand Slam semifinal, responded by slamming it straight into the top of the net. On the next point, Pennetta hit an unforced error from the backhand side.
Leading 5-2, Azarenka won the first three points despite a serve that never got above 93 mph. Pennetta hit winners off the next two points, then, finally, Azarenka closed it out with an easy putaway at the net.
Pennetta, who in 2009 became the first Italian woman to crack the top 10, made it this far a year after sitting out the U.S. Open while recovering from wrist surgery that dropped her as low as No. 166. She beat four straight seeded players and didn't lose a set en route to the semifinals.
But in what was arguably the biggest match of the 31-year-old's career, her serve was a mess. Pennetta got 44 percent of her first serves in and won only 48 percent of those points. She had a total of three game points over her nine service games and won only one of them, which gave her a 2-1 advantage in the first set.