The No. 1-ranked Nadal compiled a 35-20 edge in winners while making only 19 unforced errors Friday.
Del Potro pulled up with a hip complaint as he trailed 2-1 in the first set against Nadal, but despite clear discomfort, he fought on and made it a dogged affair until surrendering a break that gave the world No. 1 an advantage.
"Even if it was 6-3 6-4, it was an uncomfortable match for me", Nadal said.
The 24-year-old Thiem, the youngest man since Nadal to reach the final in Paris, ended the contest on his first match point with a forehand victor. Nadal is 49-2 since 2017 when playing on clay.
Thiem led 6-3 but suddenly lost focus.
Converted to dollars, the French Open's total offering comes out at $46.3m - ahead of Wimbledon's $45.6m and the Australian Open's $44.5m.
He didn't stop there, such was his extended praise for the recently turned 32-year-old.
The 16-year-old McNally, who is unseeded, beat Iga Swiatek of Poland 3-6, 7-6 (6), 6-4.
Thiem does indeed have punching power: both with his serve and his groundstrokes, with the forehand doing most of the damage. Thiem also has momentum on his side, having won their last meeting at the Madrid Open.
Rafael Nadal tries to win an 11th title at the French Open against Dominic Thiem, the only man to beat the top-ranked Spaniard on clay this season. Del Potro, who has struggled with injury, recently, may find it tough to stick with the Spaniard physically and won't have what it takes to knock off the King of Clay. "I can say a lot of things, but the easiest answer and the real answer is to play well". Because being No. 1 without a Grand Slam, I always said, is not like everything, not 100 percent.
But they face stiff competition in the final against Pierre-Hugues Herbert and Nicolas Mahut. Halep, after claiming her maiden Grand Slam title.
After dropping the first two sets he played in the opening round, Cecchinato came back to win that match in five sets, then proceeded to string together upsets.
It was the Austrian's third consecutive appearance in the semifinals at Roland Garros. In the last two editions of French Open (2016 and 2017), he lost to eventual winners Serbia's Novak Djokovic and Nadal. Their semifinal is later Friday. A victory over Thiem would allow him to equal Margaret Court's career record of 11 singles titles at a single major tournament. There is no reason he shouldn't be physically ready to go toe-to-toe with the top seed.
Baez defeated Thiago Seyboth Wild of Brazil 6-2, 6-2, while Tseng advanced past second-seeded Sebastian Korda of the United States 6-2, 7-5 in the semifinals.
Nadal beat the Argentinian in straight sets 6-4 6-1 6-2 in his French Open semi-final showdown.
In the clay court season, Nadal has already picked up his 11th title at the Monte-Carlo Masters and the Barcelona Open and an eighth trophy at the Italian Open.
"They are the first set is everything, and the weather is everything". If you were laying odds at the beginning of the tournament, Thiem was nowhere near the seventh favorite (he's seeded No. 7).
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Cecchinato had never won a Grand Slam match until this tournament.