She further proved her credentials with a dominant, yet gutsy, win over 2016 champion Muguruza, who failed to hold serve in the first set.
Looking at clay data from the last 12 months, it is the underdog, Stephens, who has the better data on serve, holding 72.9% to Halep's 71.7%, but Halep enjoys a much bigger edge on return, breaking opponents 53.5% of the time, compared to Stephens' 45.5%. After sitting out almost a year because of surgery on her right foot in January 2017, she has soared up the rankings and now made it to her second major final in the past nine months.
World No.1 Halep was defeated in the Roland-Garros final in 2014 and again previous year but will have a chance of making it third time lucky in Paris when she faces Stephens on Court Philippe-Chatrier at 2pm.
She endured an eight-match losing streak after leaving NY, going 0-6 for the rest of 2017 and then 0-2 to begin 2018, including a first-round loss at the Australian Open. When Stephens is keeping the ball in play and aggressive defensively, she's one of the tougher players on tour to beat.
Stephens closed in on her second Grand Slam title by beating pal Madison Keys 6-4, 6-4 on Thursday in the first all-American semifinal at the French Open since 2002. Virginia Ruzici won at Roland Garros in 1978.
"I'll come here tomorrow, have a hit, have lunch here, go to my room, watch TV, wait till dinner, have dinner, go to sleep". So it was very nice to play like that.
She has acknowledged having trouble handling her nerves, which is part of why she was so proud about the way she overcame Kerber, a two-time major champion and former No 1. That's why I got angry with someone. Stephens won 71 percent of her total service points and had just 11 unforced errors.
But from 0-2 down in the second set, Halep was able to change the flow of the match.
Wimbledon begins in about three weeks' time, and Halep can certainly translate her offense-defense combination to grass. "I just try to stay calm and play my game".
A first-ever Grand Slam final defeat in straight sets for Halep looked likely as soon as Stephens claimed the first game of the second set on her fourth break point. This is Halep's third final appearance in the French Open. Although Halep leads the head-to-head match-up, this is the final of a major.
That kind of inconsistency was never going to be enough to stop Stephens, who held on to an early break in the third game to serve out the first set - though Keys could consider herself unlucky after the forehand victor from Stephens on break point was later revealed to be long by Hawkeye.
Halep was my pick to win the French Open before the tournament, even though I picked against her in the Muguruza match. We saw that in last year's U.S. Open-she came right out of the gates firing on all cylinders. She's always very strong on the court. I'm backing Halep to win in three sets.