Maybe, just maybe, Rafael Nadal was a tad vulnerable, the thinking went before this French Open.

He had lost three times on his beloved red clay already this year, more defeats than he ever had on the surface before heading to Roland Garros.

Nadal and the King

The king of Spain has abdicated his throne, and the "King of Clay" wants to say thanks for everything.

King Juan Carlos announced Monday he will step down in favor of his son. A few hours later, Rafael Nadal won his record 63rd match at the French Open to reach the quarter-finals for the ninth time in 10 years.

"Well, we were very surprised by this announcement," Nadal said through a translator. "The only thing I can do is to thank his majesty, the king, for everything he did all these years.

"He was a wonderful person, a great representative of our country everywhere in the world, and Spain should thank him for everything he did during his reign. I just want to thank him for everything he did for my country."

The king, who turned 76 in January, said Monday in a nationwide address that 46-year-old Crown Prince Felipe is ready to succeed him and will "open a new era of hope."

"I think this will be a good successor to our king, our supreme leader for so many years," Nadal said. "He would be the perfect person because he's very close to the people. He's been preparing to become the king for quite a long time."

Nadal has won a record eight French Open titles and holds a 63-1 record at Roland Garros. On Monday, he beat Dusan Ljovic of Serbia 6-1, 6-2, 6-1.

The top-seeded Nadal's next opponent will be another Spaniard, fifth-seeded David Ferrer. He defeated 19th-seeded Kevin Anderson of South Africa 6-3, 6-3, 6-7 (5), 6-1.

Ferrer had less to say about the king's announcement.

"It's not my decision," he said in English with a laugh. "It's OK, no? I'm OK. I don't have any problem about the kingdom."

But Nadal was much more effusive in his praise of the king, a man he has met on many occasions over the years.

"On a personal note, he was always very nice to me, very warm. He made me feel very comfortable each time we met," Nadal said. "So I feel honoured. I had the opportunity of meeting him, and I wish him the best for the future, for whatever he decides to do for the future."

- The Associated Press

Then came an admission, after the Grand Slam tournament's third round, that his back was bothering him and slowing his serves.

Well, leave it to the eight-time French Open champion's upcoming quarter-final opponent — 2013 runner-up David Ferrer, one of the men who beat Nadal on clay this spring — to set the record straight.

"Rafael," Ferrer said, "is always the favourite."

Nadal certainly looked the part in the fourth round Monday, when he won 18 points in a row during one stretch en route to beating 83rd-ranked Dusan Lajovic of Serbia 6-1, 6-2, 6-1 for a record 32nd consecutive victory at the French Open. That broke Nadal's own mark of 31 and moved him a step closer to a fifth straight title in Paris.

The No. 1-ranked Nadal, now 63-1 for his career at the tournament, has won all 12 sets he's played in Paris in 2014, dropping a total of 23 games. He was asked whether he would have preferred a more taxing encounter by now.

"You never know what's better," replied Nadal, whose audience at Court Philippe Chatrier included musician Prince. "But, in theory, the theory says that it's better [to] win like this than win longer matches."

And his back? The one that flummoxed him during a loss in the Australian Open final in January, and then acted up Saturday, leading to an average first serve of 102 mph (165 kph) and top speed of 114 mph (184 kph)? It didn't appear to be as much of an issue against Lajovic: Nadal averaged 107 mph (173 kph), with a high of 119 mph (192 kph).

"My back can be pretty unpredictable," said Nadal, who wore thick vertical strips of athletic tape under his shirt. "I'm not lying. It's totally unpredictable. I don't want to speak too much about it."

OK, then.

Now he takes on No. 5 Ferrer, who eliminated No. 19 Kevin Anderson of South Africa 6-3, 6-3, 6-7 (5), 6-1.

Last year's French Open final is one of 21 losses for Ferrer in 27 matches against fellow Spaniard Nadal. But Ferrer won their most recent meeting in straight sets, on April 18 at the Monte Carlo Masters.

As Ferrer himself noted, though, that was a best-of-three-set match. They'll be playing best-of-five on Wednesday.

"Tactically, I will have to be perfect," Ferrer said. "I hope that I will instill some doubts in Rafa's mind, but if we play at our best level, both of us, he will be a better player."

The other quarter-final on the top half of the draw will be Wimbledon champion Andy Murray against 23rd-seeded Gael Monfils of France.

No. 7 Murray beat No. 24 Fernando Verdasco of Spain 6-4, 7-5, 7-6 (3) in a match marked by a wild third set. Verdasco held to get within 4-3 with an apparent service winner, but chair umpire Pascal Maria said that point should be replayed because a line judge called the ball out. That prompted Verdasco to begin berating Maria, shouting "Are you kidding me?" and saying he wanted a tournament supervisor to intervene — until Murray conceded the point.

Later, Verdasco said he's had several bad experiences with Maria.

"He's not the kind of umpire I get along with, I can tell you that," Verdasco said.

Monfils advanced with a much more staid 6-0, 6-2, 7-5 win against 41st-ranked Guillermo Garcia-Lopez of Spain.

Two women's quarter-finals will be No. 4 Simona Halep of Romania vs. 2009 French Open champion Svetlana Kuznetsova of Russia, and 2012 runner-up Sara Errani of Italy vs. No. 28 Andrea Petkovic of Germany.

"I played aggressive," Halep said after defeating the last American singles player left in the tournament, No. 15 Sloane Stephens, 6-4, 6-3. "I dominated the match, I think."

Petkovic's 1-6, 6-2, 7-5 victory over 148th-ranked Kiki Bertens of the Nertherlands was the only three-setter for women on Monday, a two-hour struggle filled with 77 unforced errors and 14 service breaks.

Afterward, the well-read Petkovic conducted that rare sports-event news conference sprinkled with references to Nietzsche, Sartre and Camus.

During an earlier on-court interview, Petkovic's explanation of how she turned the match around was less, well, worldly: "I told myself, `Andrea, shut up and play aggressively.'"

Canada's Nestor ousted in doubles

Toronto's Daniel Nestor and Serbian partner Nenad Zimonjic have been eliminated from the French Open following a 6-7 (2), 6-3, 7-6 (5) quarter-final loss to Marin Draganja of Croatia and Florin Mergea of Romania.

Draganja and Mergea upset the third seeds, winning a third-set tiebreaker after trailing 4-1.

Nestor had been bidding for a seventh Paris semifinal appearance.

He and Zimonjic won the opening set but were broken late in the second set for 3-5.

After Draganja and Mergea tied the match at a set apiece, Zimonjic was broken to start the third.

They got the break back for 4-all but were unable to prevent the tiebreaker.

Defending champions Bob and Mike Bryan lost in the men's doubles quarter-finals, beaten 6-4, 6-2 by the 12th-seeded duo of Marcel Granollers and Marc Lopez of Spain.

The Bryan twins, who were seeded No. 1, have now failed to reach the final at any of the last three Grand Slam tournaments — after winning four major titles in a row before that, starting at the 2012 U.S. Open.

Their bid for the first calendar-year Grand Slam in men's doubles since 1951 ended with a semifinal loss at last year's U.S. Open. The Bryans then lost in the third round at the Australian Open in January.

The brothers own a record 15 major doubles championships, including at Roland Garros in 2003 and 2013.

Halep knocks off Stephens

In the women's tournament, fourth-seeded Simona Halep of Romania beat Sloane Stephens of the United States 6-4, 6-3, and 10th-seeded Sara Errani of Italy defeated sixth-seeded Jelena Jankovic of Serbia 7-6 (5), 6-2.

Earlier, Andrea Petkovic overcame an inconsistent serve and unseeded Kiki Bertens to reach the quarter-finals with a 1-6, 6-2, 7-5 victory.

The 28th-seeded German was broken three times in the first set, once in the second and three more times in the third. But she was able to earn seven breaks of her own — all in the final two sets — to advance to the quarter-finals at Roland Garros for the second time in her career.

Bertens, a Dutchwoman ranked No. 148, had been bidding to become the lowest ranked woman to reach the French Open quarter-finals since the field at the clay-court major was expanded to 128 players in 1983.

After splitting the first two sets, the players exchanged breaks quickly and often in the third. Each of the first five games went to the returning player, with Petkovic finally holding to lead 4-2.

Both players were broken once more, but Petkovic was able to hold in the last game with a forehand winner on match point.

"It was super tough, because I didn't know her at all," Petkovic said. "I just stalked her on YouTube yesterday the whole day, and I was already impressed yesterday."

With files from The Canadian Press