For the second straight Friday, Rafael Nadal played a match against a fellow Spaniard that, on paper, appeared to be a foregone conclusion. For the second straight Friday, it was Rafa himself who was gone by the end of the day. Last week in Monte Carlo, he lost to David Ferrer on clay for the first time in 10 years, at a tournament where he's the eight-time champion. Today in Barcelona he lost to Nicolas Almagro for the first time on any surface, at a tournament where he had won 41 straight matches. Before his 2-6, 7-6 (5), 6-4 quarterfinal win, Almagro was 0-10 against Nadal.

Almagro also did it against a better version of Rafa than the one who had gone out so tamely in Monte Carlo. Nadal started this match firing the ball with confidence up the lines, and it was clear that he had paid special attention to his backhand, a shot that hurt him last week. Today he hit his two-hander well for most of the afternoon; a healthy percentage of his 22 winners came from that side. When he sent one down the line for a winner, and held to close out the first set, 6-2, it looked like he was on his way to putting Monte Carlo in the rearview mirror and righting himself for the weekend and beyond.

Six games into the second set, it still looked that way. With Almagro serving at 3-3, Nadal cracked another backhand winner to get to deuce, and then earned three break points. On the first two, he put a backhand into the net and a forehand into the net; on the third, Almagro, beginning to look a little more emboldened and determined than he normally does when he plays Rafa, smacked an unreturnable forehand and went on to hold.

Yet six games after that, Nadal still appeared to be in control. Down 1-3 in the tiebreaker, he moved ahead 4-3 with a second-serve ace that completely fooled Almagro. But that would be the last time Nadal would be a step ahead. The turnaround came at 4-4 and 5-5 in the breaker. On the first of those points, Rafa sent what should have been a winning forehand over the baseline. On the second, Almagro clipped the back of the baseline with a backhand; the ball skipped forward and Nadal couldn’t handle it. Almagro took advantange of his rare good fortune against Rafa by closing out the set with a forehand winner. It was the first set Nadal had lost in Barcelona in since 2008, and the first set he had lost to Almagro since 2010.

Things went a little haywire in the third set, as the two traded winners, errors, and breaks back and forth at lightning speed—there were nine breaks in total in the match. Almagro appeared to be in control when he broke with a crosscourt forehand winner for 4-3. A few minutes later, Nadal appeared to have restored order when he broke with a strong forehand return of a second serve, a shot he typically struggles with on important points. Soon after that, though, Almagro recovered to break serve at love with a series of unstoppable winners—his ability to shake off the break at 4-3 and bring his his best stuff again at 4-4 might have been the biggest surprise of the day.

That is, until the next game. Almagro walked out for what may have been the biggest service game of his career at 5-4; to the shock of no one, he immediately went down 15-40. At 30-40, Nadal worked the rally to his favor, lined up the simplest of inside-in forehands, and...hit it into the tape. Almagro, now fully emboldened and determined, seized the first chance he has ever had to beat Nadal with one last forehand winner, hit 36th ground-stroke placement of the day.

Then Nico briefly went berserk. Some thought his celebration was over the top; I say, let him slide for today, he may never have a better moment on a tennis court.

Nadal, while he committed 24 errors and missed a key easy forehand at the end of each of the last two sets, was more aggressive than he had been last week, and seemed to be hitting the ball better. His problem was break points: He was five of 18 on them. And his problem was Almagro, who took the court position away from Rafa as the match went along, and who stopped missing the shots he normally misses at crucial stages. He outplayed Nadal at the end of the second-set breaker, and in the last two games of the match.

Nadal has now lost in the quarterfinals in Monte Carlo and Barcelona, both times to a fellow Spaniard. That’s about as unforeseen as developments go in sports these days. Or is it? Afterward, Portuguese tennis journalist Miguel Seabra said he thought Rafa has “introduced positional and technical changes in his game to better face Djokovic, but it’s affecting him vs. others.” I haven’t noticed that, but it’s possible, and it’s something to look for.

What I immediately thought today was how much Nadal’s 2014 is beginning to resemble Roger Federer’s 2010. That year Federer, who was 28 and had finished the previous season at No. 1, lost for the first (and for the most part only) times in his career to Marcos Baghdatis, Ernests Gulbis, Albert Montanes, Robin Soderling, and Gael Monfils; he also lost twice to Tomas Berdych, who hadn’t beaten him in six years. So far in 2014, Nadal, who will be 28 in June and was No. 1 last season, has lost for the first time to Stan Wawrinka, Alexandr Dolgopolov, and Nicolas Almagro, and for the first time  in 10 years on clay to David Ferrer. In 2010, Federer was very close to winning in four of those defeats; in 2014, Rafa was close to winning against Dolgo and Almagro.

Rafa’s slump has not yet gone as deep as Federer’s went in 2010. But in both cases, they show, in case you somehow had forgotten after watching these guys win for so long, that (1) the difference between victory and defeat is paper thin, and (2) when you start to lose the close ones, the other guys will be watching, and they'll remember. Today, at 5-5 in the tiebreaker, a ball landed on the back of the line for Almagro, instead of landing an inch beyond it. At 4-5 in the third set, a putaway forehand caught the tape for Nadal at break point, instead of going over it by an inch. Because of that, Almagro moves on to the semis, while Nadal will go back to searching for that missing inch. We'll see in the coming weeks who was watching.