Halep had never advanced beyond the fourth round of a Grand Slam event before the Australian Open earlier this year. She reached the quarterfinals in the season's first major, which continued the upward trend the 22-year-old Romanian rising star has been on since the latter stages of 2013.
She was eliminated by eventual finalist Dominika Cibulkova in an anticlimactic straight-sets match. Yet, it was a learning experience for Halep because at that point in a major tournament it's easy to start thinking about the title instead of focusing on every match.
When I reached the quarters in Australia this year, I didn't know how to manage my emotions before the match. I was very nervous on court and I couldn't play my game. This time I was very relaxed and it was a perfect day. So now I feel good. I feel my game. I feel prepared for the next match.
She certainly didn't seem nervous on Thursday against Petkovic, who was also making her first appearance in a Grand Slam semifinal.
Halep rushed out to an early lead with a break and a hold to make it 2-0. It was just the start of what developed into a tremendous set of tennis from the rising star.
She defended her serve, moved around the court smoothly and attacked off both wings. Her solid play forced Petkovic to take more chances looking for outright winners because most of the points that got to neutral were being won by the No. 4 seed.
In turn, Halep captured the first set 6-2 in just 28 minutes. She had 12 winners compared to Petkovic's three. She also converted 2 of 4 break opportunities while the German veteran didn't generate a single break chance.
ESPN Tennis noted the opening set maintained a trend of Halep making quick work of opponents in the tournament so far:
Early in the second set, Tom Perrotta of the Wall Street Journal provided a glimpse at the fourth-ranked player's pursuit of perfection:
Petkovic tried to mount a rally in the second. An early break and a couple holds allowed her to grab a 3-1 lead as the unforced errors from the first set were suddenly clipping lines.
Halep immediately battled back to get back on serve at 3-3. Simon Cambers of The Tennis Space praised the overall level of play as the second set wore on:
They traded holds the rest of the way, sending the set into a tiebreak. Halep seized control by charging out to a 4-1 lead before Petkovic got it back on serve at 4-3. A costly error by the No. 28 seed gave Halep the mini-break back, however, and she never relinquished the lead to close it out 7-4.
Piers Newbery of BBC Sport noted Halep didn't lose a set en route to the title match:
Looking toward the final, Halep will go up against 2012 French Open champion Maria Sharapova, who beat Eugenie Bouchard in the other semifinal. She has lost all three of their prior meetings, including one on clay in Madrid during the build-up to Roland Garros.
Given those head-to-head numbers and Sharapova's recent success in Paris, she will likely be the favorite despite being the lower seed. That said, it should be a competitive match just like the one in Madrid that went three sets.
A win would move Halep to the forefront of women's tennis alongside the likes of Sharapova, Serena Williams and Li Na. Even if she loses, however, she's done enough in the season's first two majors to believe big things are ahead.