Del Potro said the Austrian, the only player to beat Nadal on clay over the past two seasons, has a chance - albeit a slim one. Both men are at stages in their career that have previously been points of great decline for the greats who came before them.
He buckled at 5-5 though and sent a backhand long on break point, leaving Del Potro to serve for the match, which he did easily as Cilic sent three more backhands out.
Spain's Nadal will meet Dominic Thiem in Sunday's final.
By the absurd standards Nadal has set here, even facing those break points amount to a lapse, as does the opening set he dropped to the terrier-like Diego Schwartzman in the quarterfinals.
Nadal thrashed the Argentine to win the match in straight sets: 6-4,6-1,6-2.
Thiem withstood huge challenge from Italian underdog Marco Cecchinato in the first two sets of Friday's semifinal, winning 7-5 and 7-6 (10) respectively, before easing through the third set 6-1.
-When you buy Tennis Channel Plus, your 12-month subscription gets you access to every ATP Masters 1000 tournament played outside the US, and every round through the finals of WTA Indian Wells, Miami and Cincinnati. "I can say a lot of things, but the easiest answer and the real answer is to play well". I have been on court just couple of minutes ago. I feel very fortunate to play in front of this crowd. If he wins the game, OK.
"We know Thiem can beat him", Cash said.
Schwartzman compiled a 20-4 edge in winners for the set, closing it with a forehand that landed right at the baseline.
"He is a nightmare opponent for Nadal", Wilander said about Del Potro, as quoted on Tennis World USA. He missed the tournament every year from 2013-16 because of injuries, including three operations on his left wrist.
"He's a big favorite against anybody", Thiem said of Nadal. "His game is too good for me".
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If there were odds on blocked shots, I'd lay the house on Washington . "There's no side entrance that you can get into. We're just focused on the next one. "Last game was definitely a step in the right direction to how we can play".
"In every game that I served, I had problems".
Thiem insists he has a "plan" against Nadal, one which he hopes translates to the longer best-of-five set format.
Thiem had three set points at 6-3 but Cecchinato quashed them all and reversed a triple of set points in his favor, but he couldn't convert a tiebreaker win this time as Thiem moved ahead after two errors.
Nevertheless, the 24-year-old can look back on two victories over Nadal on his favourite surface in the last 13 months, including one in Madrid just last month. He lost to eventual champions Novak Djokovic in 2016 and Nadal in 2017.
Romania's Simona Halep will first play American Sloane Stephens in the women's singles final tomorrow.
This time, Thiem instead faced Cecchinato, who never had won a Grand Slam match until this tournament and was the lowest-ranked men's semifinalist at the clay-court major in 19 years.
"It was not a very nice feeling", Thiem said.
The Spaniard maintained his momentum to take a 2-0 lead in the second, executing the drop shot to perfection and making Del Potro run in the heat, claiming another break with a searing backhand.
The No. 7-seeded Thiem beat Cecchinato 7-5, 7-6 (10), 6-1 in the semifinals Friday.
Thiem sent Cecchinato scurrying around the court before breaking decisively for a 6-5 lead with a lovely forehand victor.