But the 33-year-old Spaniard began finding his form at last month's Italian Open, beating Djokovic in that final. That's great to see.
The pair have not played each other at Roland Garros since Nadal's victory in the final eight years ago, his fifth from five French Open matches against Federer. Thiem had it even easier, dusting No. 10 Karen Khachanov of Russian Federation 6-2, 6-4, 6-2.
That was to take nothing away from her opponent, who played like the more experienced competitor and clinched a place in her first slam final with a typically precise backhand drop shot, winning 7-5 7-6 (2).
World number one Djokovic reached his ninth Roland Garros semifinal, sweeping past Alexander Zverev, keeping his bid to become just the second man to hold all four Slams at the same time twice firmly on track.
Federer went four and a half years between major titles from to 2012 to 2017.
Saturday's final will be the youngest final at a Slam since the 2008 Roland Garros championship match when 20-year-old Ana Ivanovic defeated Dinara Safina, 22.
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He has had a 30-in-a-row (2015 Wimbledon to 2016 Wimbledon-the record), a 27-in-a-row (2011 Wimbledon to 2012 French Open) and now a 26-in-a-row (2018 Wimbledon to 2019 French Open). But Federer was more hesitant against his nemesis, and Nadal won 6 of 13 return games.
She's played 12 main tour semi-finals, winning eight, including both this season, while Anisimova's two WTA semi-finals have come in lower-profile global level events, in Hiroshima in September 2018 and Bogota in April this year - certainly Barty has more experience of the bigger stages.
Fernandez, who lost in the Australian Open final, will face No. 8 seed Emma Navarro of the United States for the French Open title.
Nadal has downplayed the significance of the contest, saying: "What I will do is try to do my best, so that the victories I have won on this surface against him count for something. Yeah, I mean, it's insane", said Anisimova, who was born in New Jersey to Russian parents and moved to Florida when she was 3. I don't think you know quite what to expect tomorrow, but I will prepare and do the best that I can to keep it normal.
Briton Johanna Konta, who lost her semifinal to Marketa Vondrousova of the Czech Republic on Court Simonne-Mathieu, was among those critical of the scheduling, especially when she was asked if it felt like a Grand Slam semifinal.
The men have also made a combined 80 major finals (the women none) and 760 weeks at No. 1 (the women none).