Watching the men in Barcelona and the women in Stuttgart on Sunday, I started to wonder: Which is more impressive, that Rafael Nadal won his eighth title at his second clay-court event—Barcelona joins Monte Carlo on the top line of his résumé of destruction—or that Maria Sharapova, who defended her title on red clay in Stuttgart, has improved her game so drastically on her least-favorite surface in the middle of her career? The question stayed in my mind as Nadal and Sharapova completed their championship-winning runs with identical 6-4, 6-3 final-round wins.

The answer, when you take the long view, has to be Nadal. His title records at the spring clay events are already likely to stand for decades, and he doesn’t appear to be anywhere close to being finished. Four months ago, many were wondering if he would ever be the same after his latest round of knee problems, even on dirt—I seem to remember Andy Murray mumbling something about having a shot at the French Open. This past week, despite having to play twice in one day and getting off to slow starts in three different matches, Nadal won Barcelona without dropping a set. On one level, his comeback has been amazing, even for a top player and future Hall-of-Famer; Nadal currently leads the ATP in tournament titles in 2013, with four. On another level, though, a Nadal win on clay is about as routine as any in sports at the moment. To most people, he’s just doing what he was born to do.

That can’t be said for Sharapova. She’ll never approach Rafa’s clay record, or his masterful movement on the surface, but like him she's in the process of doing something rare for an athlete on it. Players can get better with age, but even the best struggle to turn weaknesses into strengths, or to smooth over flaws completely. In the Stuttgart final, Sharapova showed that, at least for the moment, she has pulled it off on clay.

Sharapova has admitted in the past that she didn’t know how to move on the surface, but against Li Na on Sunday Maria won by making sliding gets, and turning those defensive plays into winners a few shots later. “Going from defense to offense,” as the cliché goes, is a key to any clay-courter’s game, but it's not one that has been associated with the long-limbed and less-than-agile Sharapova in the past. It’s one thing to make tactical or technical changes to your game, but it’s another to make physical changes, to make yourself a better defender who can track down more shots. To that end, Sharapova seems to have learned a trick from Novak Djokovic: She saved a quite a few points this week by stretching wide and blocking a hard-hit ball back with her backhand, goalie-style. As you could see at the end of each of her matches, Maria the fashion maven is willing to get her sneakers dirty to get better.

For two players who personify fire and ice in tennis, Sharapova and Nadal have their similarities. They’re both 26. They each won their first majors very early—Sharapova at 17 at Wimbledon in 2004; Nadal at 18 at Roland Garros in 2005. They’ve been persistent enough to complete career Grand Slams and have reached No. 1, but they’ve also had injury troubles that have kept them away from the game. And while they’re both major stars in their own rights, they’ve also labored in the shadows of two older legends, Serena Williams and Roger Federer.

When they were young, Sharapova and Nadal were often compared for their tenacity. It was said that neither of them ever gave away a point. That’s not technically true; I’ve seen both Rafa and Maria throw away a 40-0 point or two over the years. However much they loved to fight as kids, they’ve learned that certain points mean more than others. But the comparison is apt. What sets Nadal and Sharapova apart is their ability, psychologically, to outlast their opponents. Each of them showed that again this past week.

It was obvious in Sharapova's case. It took her three sets to win each of her first three matches, against Lucie Safarova, Ana Ivanovic, and Angelique Kerber, respectively. Maria didn’t look like the superior player in any of those contests. She let leads slip in all three, and good stretches of play were followed by bad. Yet it was hard to imagine her losing any of them. That wasn’t just because she was the higher-ranked player; it was part of the effect that Sharapova has on court. You feel like she can lose because she doesn’t play well, but never because she’ll cave at any stage. Maria never takes a mental vacation, and very rarely lets one bad game turn into two or three. That’s harder to do than it looks. It’s often said that Serena Williams goes out of her way to beat Sharapova as badly as she can to avenge her loss to Maria in the 2004 Wimbledon final. Judging by Serena’s own comments, though, she's extra motivated and vigilant against Sharapova because she knows the Russian won’t go away on her own. (It should also be noted that, as great as Maria’s clay game has been these last two seasons, she lost her only match to Serena on the surface last year, in Madrid. A rematch in the Caja Magica in a couple of weeks would be more than appropriate.)

Nadal didn’t need as much psychological stamina in Barcelona, but it was still a key to his win over Nicolas Almagro in the final. He came back from a two-break deficit in the first set, but just as impressive, and characteristic, was the way he put the match away in the second. Up 2-1, he fell behind 40-15 on Almagro’s serve. It looked like it was going to be a routine hold, but Nadal refused to give up on the game. He hung around and watched Almagro, who is now 0-10 against Rafa, make a couple of errors, and finally capitalized with a break. What had been a close set two points earlier was suddenly all but over.

Maria and Rafa each won their first top-level tour events of the year at Indian Wells, and they won their first events of the spring clay season on Sunday. You get the feeling those won’t be the last. Right now a little dirt looks good on these two stars. In Nadal’s record on the surface, and in Sharapova’s hard-earned slides across it, they continue to push the limits of what we think is possible in tennis.