PARIS -- Rafael Nadal's back is giving him more trouble than his opponents so far at the French Open.
After pushing his winning streak at Roland Garros to 31 matches with a 6-2, 7-5, 6-2 victory over 65th-ranked Leonardo Mayer of Argentina in the third round Saturday, eight-time champion Nadal said his bothersome back is forcing him to cut back on the velocity of his serves.
Nadal's back also acted up in January during his loss to Stan Wawrinka in the Australian Open final.
"During my career, I had (a) few problems. ... Hopefully will not be (the) case" the rest of the way in Paris, the No. 1-ranked Nadal said.
"I served more slowly since I started feeling the pain," he said, noting that he's worn tape on his back for extra support.
Against Mayer, Nadal averaged only 102 mph (165 kph) on first serves, with a top speed of 114 mph (184 kph). That was down from an average of 111 mph (179 kph) and top of 122 mph (197 kph) in the first round against Robby Ginepri last Monday.
Through six sets across his first two matches, Nadal faced only five break points and lost serve only twice. He needed to deal with eight break points against Mayer, losing two.
Still, Nadal made only 10 unforced errors all match -- two in the first set, three in the second, five in the third -- and equaled his longest run at Roland Garros.
But the last time Nadal won 31 in a row in Paris, he failed to get No. 32, losing in the fourth round in 2009 to Robin Soderling. That remains the Spaniard's only defeat in 63 matches at the tournament.
Nadal has dropped 19 games heading into his match against 83rd-ranked Dusan Lajovic of Serbia, who is in the second major of his career and beat Jack Sock of the United States 6-4, 7-5, 6-3. Another American, Donald Young, lost in five sets to Guillermo Garcia-Lopez of Spain, leaving No. 10 John Isner as the last U.S. man in the field.
Before this French Open, the 23-year-old Lajovic had a 10-21 career record in tour-level matches, never winning two in a row.
"I saw him play a few times on TV. Sure, it's great to have new players on tour, young players on the tour that are coming strong. Hopefully not too strong," Nadal said with a smile. "We'll see on Monday. I hope to be ready."
Asked whether he would seek advice from another Serbian, No. 2 Novak Djokovic, before facing Nadal, Lajovic joked: "Yeah, I will try to ask everybody (for) some tips."
That won't help if Nadal produces shots of the sort he did when Mayer served at 5-all in the second set -- a stretching, scooping backhand lob to break.
As Mayer watched the shot sail overhead, he waved his left hand to signal to the ball to go out, then rolled his eyes when it curled in. At the other end, Nadal pumped his fist, ahead 6-5 and well on his way to reaching the fourth round for the 10th time in 10 trips to Roland Garros. Roger Federer is the only other man to make it to the final 16 in Paris that many years in a row.
The man Nadal beat in last year's final, No. 5 David Ferrer, defeated No. 32 Andreas Seppi of Italy 6-2, 7-6 (2), 6-3. Ferrer now plays No. 19 Kevin Anderson of South Africa.
No. 23 Gael Monfils of France put together a 5-7, 6-2, 6-4, 0-6, 6-2 win over No. 14 Fabio Fognini of Italy in a wild match that included a point penalty for Fognini when he threw his racket and it landed near a ball boy. Monfils and Fognini combined for more than twice as many unforced errors, 137, as winners, 66.
Earlier Saturday, No. 15 Sloane Stephens moved into the fourth round for the sixth major in a row. The American now meets No. 4 Simona Halep of Romania. Other fourth-round matchups: 2009 champion Svetlana Kuznetsova against No. 23 Lucie Safavora; 2012 runner-up Sara Errani against No. 6 Jelena Jankovic; No. 28 Andrea Petkovic against 148th-ranked qualifier Kiki Bertens of the Netherlands.
As the sun came out and the temperature topped 70 degrees (20 Celsius) after several days of overcast skies and occasional rain, Stephens eliminated No. 22 Ekaterina Makarova of Russia 6-3, 6-4, while Halep beat 55th-ranked Maria-Teresa Torro-Flor of Spain 6-3, 6-0.
Halep is the highest seeded woman left, because of losses by No. 1 Serena Williams, No. 2 Li Na and No. 3 Agnieszka Radwanska.
Said Halep: "That's a surprise for everyone."