Simona Halep vs. Flavia Pennetta: Score and Reaction from 2015 US Open

After 15 years as a professional, 33-year-old Flavia Pennetta has finally reached the first Grand Slam final of her career as the Italian underdog defeated No. 2 Simona Halep 6-1, 6-3 Friday at Arthur Ashe Stadium in New York City.

The 26-seeded Italian was dominant from start to finish as she improved her career record against Halep to 4-1 and cashed in on her second career trip to the U.S. Open semifinals.

In addition to a career first, Pennetta made some history by beating her 23-year-old opponent, per ESPN Stats and Info:

The wily veteran made it clear just how important the win was for her after so many attempts to reach this point, according to U.S. Open Tennis on Twitter:

Despite Pennetta's past victories against Halep, Friday's performance was somewhat unexpected due to the Romanian's success on hard courts:

With the victory, Pennetta will meet countrywoman Roberta Vinci in the final following Vinci's shocking upset over world No. 1 Serena Williams.

Considering how consistent Halep has become over the past couple of years, most probably expected her to come out firing Friday. But that wasn't the case as seemingly nothing went right in the opening set.

After holding her first serve of the match to make it 1-1, Halep went haywire as she proceeded to lose the next five games in a row and dropped the opening set 6-1.

According to Craig O'Shannessy of the New York Times, the Romanian favorite's attempts to end rallies early backfired:

Per Steve Tignor of Tennis.com, that led to Halep making an inordinate amount of unforced errors:

That isn't to say that Pennetta didn't play well as she won 74 percent of her first serves, whereas Halep won just 45 percent of her own first-serve points.

Even so, Matt Cronin of USTA.com was fairly shocked by how out of sorts the world's No. 2 player was out of the gates:

Ben Rothenberg of the New York Times suggested that a difficult situation involving Halep's coach, Darren Cahill, could have negatively impacted her:

Halep seemed ripe for the picking after an uninspiring first set, but she started to turn things around in the second. She picked up an early break of Pennetta's serve to go up 3-1, but she wasn't able to take full advantage of it.

She handed Pennetta a break back with a double fault, which Andrew Jerell Jones of the Guardian believed was a huge mental error on her part:

The Italian then held serve and broke Halep once again to go up 4-3 and put herself on the precipice of winning a match that few gave her a chance to triumph in.

Per ESPN's Brad Gilbert, the fact that Pennetta enjoyed previous success against Halep was likely a huge contributing factor in how freely she played:

That was on full display in the latter portion of the second set as Halep seemingly couldn't buy a point, according to Rothenberg:

Pennetta mercifully put the match away on Halep's serve and punched her ticket into the final, which was an unlikely result entering the tournament since she was bounced in the first round of two of the year's first three Grand Slams.

Vinci and Pennetta have played each other many times over the years with Pennetta holding a 5-4 advantage. They traded wins and losses over their first eight career meetings, but Pennetta won the most recent one at the 2013 U.S. Open.

That was a straightforward 6-4, 6-1 victory for her in the quarterfinal, and despite Vinci's incredible win over Serena, Pennetta has to be considered the favorite entering the final.

Neither woman has ever played in a Grand Slam final before, but based on Pennetta's superior ranking and past success at the U.S. Open, she has a golden opportunity to become a major champion.

Follow @MikeChiari on Twitter.