Defending a title is never easy. Just ask Daniil Medvedev. He has 20 singles titles to his name and they’re all different. That’s to say, he’s never successfully defended a title. When the title in question is a Grand Slam, where the stakes are just that little bit higher, it becomes even more challenging. And Carlos Alcaraz is feeling the heat.

Fresh off of winning his third Grand Slam and becoming the youngest player to win one on all three surfaces, Carlos Alcaraz hasn’t looked at his 100% at Wimbledon so far. All three matches leading up to this Round of 16 encounter against Ugo Humbert have featured at least one tiebreak, which is to say he’s not had it easy. In fact, Frances Tiafoe even pushed him to five sets in the third round, but the Spaniard eventually won 5-7, 6-2, 4-6, 7-6, 6-2. And midway through the fourth set against Humbert, it looked like Alcaraz was in for back-to-back five-setters.

As opposed to the first hour-and-a-half of the match, which saw Carlos Alcaraz go up 6-3, 6-4, the third set was sort of an awakening for Humbert. In just over half an hour, the Frenchman broke Alcaraz three times to win the set, 6-1, outplaying the Spaniard in every aspect of the game. But with the possibility of a comeback looming, the nerves started to set in, not just for Alcaraz but also for Humbert.

Serving first in the fourth, Ugo Humbert couldn’t hold serve. But just when Alcaraz, his coach Juan Carlos Ferrero, and the rest of his box thought that was all the opening the 21-year-old needed to seal his spot in the quarterfinals, Humbert broke right back. But the Spaniard broke back yet again to take a 2-1 lead. And after losing 4 consecutive service games, he held serve to go up 3-1. However, Humbert wasn’t done. He held serve, broke back, and held serve again to take a 4-3 lead. That was when it looked like things started to go south for Carlos Alcaraz in the fourth.

Serving to potentially stay in the set, Alcaraz committed a double fault to go down 0-40. In stark contrast to his happy, smiling, and calm persona, he looked toward his box and screamed in frustration: “I don’t know what to do.” However, he refocused, kept calm, and saved three break points to hold his serve and level the fourth set, 4-4. After more than a set-and-a-half of watching Humbert make Alcaraz-like shots, the Spaniard regained his form, hit a couple of trademark Alcaraz shots, and eventually broke Humbert in the 11th game to serve for the match.

And that’s precisely what he did. He may have struggled, but he booked his place in the quarterfinals, keeping the dream of a title defense alive. After the match, Carlos Alcaraz said, “Playing lefties is always tricky. At Queen’s, first on grass [against Draper].” Following the French Open, Alcaraz has had a subdued preparation for the grass-court season. He played a solitary tournament in the lead-up to Wimbledon at the Queen’s Club Championships, where he lost in the Round of 16 against home hero Jack Draper.

Reflecting on his match against Humbert, he added, “Very difficult, but I just played my own game. I played at a really high level. I just had to stay in the point, show my opponent that I’m always going to be there, last ball. Now I will rest a little bit, recovering to be 100% for the next one.” The 21-year-old will face American Tommy Paul in the quarterfinals on Tuesday. Set to be another thrilling matchup, there’s no doubt Carlos Alcaraz will hope to continue using an improved aspect of his game to his advantage: his serve.

Carlos Alcaraz’s serve has been on his “to-do list” of improvements to make

Carlos Alcaraz isn’t the tallest of players, at least not compared to players he regularly competes against. More than his service games, the Spaniard has mastered the art of returning. But when it comes to matches like this, against players like Humbert who serve big, it’s crucial for Alcaraz to hold his own serve. And that’s exactly what he’s worked on to help him win close matches.

While he hit 16 aces against Frances Tiafoe in the third round, Alcaraz served 14 aces against Humbert. Explaining the massive improvement in his serve, the Spaniard said, “It’s something I’ve improved quite a lot. It’s been on my to-do list for many years: Trying to improve my serve.” In his third-round match against Tiafoe, his strong serves helped him win key moments.

He explained, “In situations like today’s, I had to try and get points from my serve. I had to make it significant, a key part of my game, at difficult moments… I’m happy to see we’ve improved it, and that we’ll continue to improve it.” With growing confidence, it’ll be interesting to see if Alcaraz can win back-to-back Grand Slam titles and defend his Wimbledon crown.