Defending champion Carlos Alcaraz survived a major scare before beating Emil Ruusuvuori in three sets to reach the Madrid Open third round on Friday but admitted he "didn't know what to do" at key parts of the match.
World number two and US Open champion Alcaraz fought back to see off the 41st-ranked Finn, 2-6, 6-4, 6-2.
"It was really tough. I would say I was about to lose," said Alcaraz who famously defeated Rafael Nadal and Novak Djokovic in Madrid last year.
"It was complicated. There were moments that I didn't know what to do."
Alcaraz, fresh from defending his Barcelona title last weekend, will face Bulgarian Grigor Dimitrov for a place in the last 16.
The 19-year-old Alcaraz hit 10 aces in his 36 winners but was forced to save nine of 11 break points in the 2hr 16min clash. Five of those came when he was 3-2 down in the second set.
"It was just one point," added Alcaraz. "One of the break points he had at 2-3 in the second set was like a match point for him.
"I was really happy I was able to save that game and come back a bit. It was really tough. Emil played unbelievably, but I am really, really happy to get through that."
In an indication of his frustration, Alcaraz speared his racquet into the court as he was staring down the barrel in the sixth game of the second set.
"I don't support that type of thing, the racquet came out and I regret it," he admitted.
In sharp contrast, women's world number one Iga Swiatek cantered to a 6-3, 6-2 win over Austrian lucky loser Julia Grabher.
Swiatek didn't play Madrid last year but that didn't dent her claycourt form as she went on to capture a second French Open later in the season.
After winning the Stuttgart title last weekend, the Pole is riding a five-match winning streak on the surface.
Swiatek will next face American left-hander Bernarda Pera who was a 6-1, 6-3 winner over Germany's Tatjana Maria.
Pera is in the third round for the first time in five years.
World number seven Holger Rune saved a match point to defeat Alexander Bublik 6-1, 4-6, 7-6 (11/9).
Last weekend's Munich champion and Monte Carlo Masters runner-up Rune saved the match point at 7/8 in the final set tie-break.
Matteo Arnaldi gained his first victory over a top-10 player as he upset third-seeded Casper Ruud 6-3, 6-4.
Arnaldi, a 22-year-old Italian ranked 105, who saved a match point against Benoit Paire in the first round, hit 35 winners on his way to a more comfortable victory over Ruud, who reached two Grand Slam finals last year.
"The ball bounces so high and I didn't like it at first. I struggled a bit," said Arnaldi.
"But today, I don't know, maybe the stadium, maybe the pressure on him, but I played the best match of my life."
Fifth seed Andrey Rublev continued his hot form as he beat Stan Wawrinka 7-5, 6-4.
Rublev started the clay season by winning in Monte Carlo and then reaching the final in Banja Luka last weekend, where he lost to Dusan Lajovic.
He needed just 77 minutes to dispatch Wawrinka, the 38-year-old Swiss triple major winner.
Rublev broke in the 11th game of the first set. He fell behind to an early break in the second before winning five straight games and then serving out for the match.
"When I saw the draw I thought that it was amazing being the fifth seed and having Wawrinka in my opening round," Rublev said.
"In the last meeting, he beat me, so I was thinking to focus and see what would happen but I was able to win today and I feel great."
Rublev will next face Japan's Yoshihito Nishioka, who beat Slovakian Alex Molcan 5-7, 6-4, 6-4.
In the women's tournament, Anna Kalinskaya, ranked 62, defeated seventh seed and Wimbledon champion Elena Rybakina 7-5, 4-6, 6-2
It was a third top 10 win for Kalinskaya who next faces 27th seed Petra Martic.
Another Grand Slam champion to exit was 15th seed Victoria Azarenka who was stunned in straight sets by Alycia Parks of the United States.
Parks, ranked at 54 in the world, has now won her last four matches against top 20 opponents.