Jannik Sinner took a first step towards a potential record fifth consecutive Masters 1000 title with a 6-7 (6/8), 6-1, 6-4 victory over Benjamin Bonzi in the Madrid Open second round on Friday.
The Italian world No 1 is looking to beat the record of four consecutive triumphs held by all-time greats Novak Djokovic and Rafael Nadal this week in the Spanish capital.
Sinner dropped only one set on the way to trophies in Paris, Indian Wells, Miami and Monte Carlo, but Bonzi battled brilliantly to claim the first at the Manolo Santana stadium.
The Frenchman survived five break points to reach a tie-break, where he also saved set point before edging ahead.
However Sinner stepped up a gear in the second set, securing breaks in the fourth and sixth games, and another in the third on his way to the third round.
"It was a tough match, I had some chances early on and I couldn't use them, but this is tennis," said four-time Grand Slam winner Sinner.
"It's not bad to start the tournament like this, two and a half hours on court, it gives me good feedback where we need to improve for the next round.
"Of course, we need to improve, but I'm also happy, when you're not playing your best tennis and win, it's still a good result."
With Sinner's biggest rival Carlos Alcaraz injured and unable to compete either this week or in the upcoming French Open, the Italian is overwhelming favourite for every competition he enters in the weeks ahead.
Earlier, Croatian qualifier Dino Prizmic sent world No 6 Ben Shelton crashing out with a 6-4, 6-7 (4/7), 7-6 (7/5) victory.
Promising 20-year-old Prizmic, ranked 87th, secured his first ever win over a top-10 player in a three-hour battle in the Spanish capital.
American Shelton triumphed at the Munich Open on Sunday on clay but was unable to force a single break point on Prizmic's serve.
Shelton's compatriot Tommy Paul also suffered a surprise early exit, falling 7-5, 6-4 against Argentine Thiago Tirante.
Spaniard Rafael Jodar, 19, who impressed with a run to the Barcelona Open semifinals last week, dumped out world No 8 Alex de Minaur 6-3, 6-1.
"Everything went very well," said Jodar. "De Minaur is a very tough opponent, and I knew what I had to do from the very beginning."