Romanian third seed Halep, the runner-up to Maria Sharapova in 2014, was thankful still to be in the tournament after her remarkable recovery from a set and 5-1 down against Elina Svitolina in the quarter-finals. Halep denied the Czech the No. 1 ranking.
On the morning of the women's French Open semi-finals on Thursday seven-times champion Chris Evert said the moment had arrived for a player to step up and seize an opportunity that may not come around again for a while. Ostapenko has a chance to win her first career grand slam title at just 20 years old. It gave me confidence.
"I never played against her".
The battle between Halep and Pliskova had more on the line than a shot at the Roland Garros title, as both were gunning for the top spot in the WTA Women's Singles Rankings.
The firebrand baseliner is the youngest player to reach a major final since Caroline Wozniacki's advance as a 19-year-old at the 2009 US Open decider.
Earlier, India's Rohan Bopanna and Canada's Gabriela Dabrowski saved two match points to claim their first Grand Slam title with victory in the French Open mixed doubles final.
The underdog Ostapenko also became the first Latvian ever to have reached the final at a Grand Slam tournament.
"I think I have the game. I have the mentality to win, but it's going to be tough".
"I think I would beat 99 per cent of the girls with the way I played today". But I'm confident as well.
"I learned many things during the years, not just after that final".
- "I am really happy". She is not one to back down.
Halep reunited with Cahill in Madrid after the Adelaide mentor walked away following her mid-match emotion in Miami.
Ostapenko celebrated her 20th birthday with a 7-6 (7-4) 3-6 6-3 win over Switzerland's Timea Bacsinszky. Ostapenko continues to go for broke and it's paying off for her in a way she couldn't have imagined.
"My game is stronger, and it's different".
With such an attacking game, backing Ostapenko could be a precarious business.
When it was, Ostapenko - who began working with retired clay-court specialist Anabel Medina Garrigues in April - also ensured becoming the youngest French Open finalist since Ana Ivanovic in 2007. "It's a great way to celebrate my birthday". "I don't need advice on how to handle pressure", said Halep.
Action is due to continue tomorrow with the men's semi-finals.
Serbian Ivanovic was honored in a ceremony on Philippe Chatrier court after Thursday's match: The 2008 champion retired in December.
With Bacsinszky serving at 3-5 Ostapenko, coiled like a spring, brought up two match points with an unstoppable backhand return that cleaned the baseline then smote a rasping forehand return victor that left her opponent flat-footed.
She benefited from Pliskova's clumsiness in the first set before the Czexch rediscovered her touch. She made 14 unforced errors against the No. 2-seeded Pliskova, whose total was 55.
During the first set of three tennis players have exchanged breaks, and at the tiebreak constantly attacked Ostapenko has played a more reliable and took the lead.
With points stretching in the third, the key break resulted at 4-3.
Bacsinszky's scouting report on Ostapenko, a pal she played doubles with past year? "I think it's a nice gift".
"After all those rallies, I was just exhausted".
"The best example is the match point".