Rafael Nadal remains on track for an elusive Paris Masters title after beating Pablo Cuevas 6-3, 6-7 (5), 6-3 to reach the quarterfinals on Thursday.
He has not reached the final since losing to David Nalbandian in his first appearance 10 years ago. Nadal improved to 4-1 overall against Cuevas and next plays Serbian qualifier Filip Krajinovic for the first time.
"He had a very successful season, winning a lot of challengers, and now he's playing well on the tour," Nadal said of Krajinovic. "When you're winning a lot of matches you're in a good dynamic."
Cuevas competed well in spells against a nervy Nadal, who was erratic on serve and made countless unforced errors in a gritty contest.
One of the most glaring came at 5-5 in the second-set tiebreaker, when Nadal hit an easy forehand into the net to give Cuevas a set point. After a brief rally, Nadal hit a backhand long and Cuevas leveled the match.
Nadal had some strapping under his right knee before the deciding set, then raced into a 3-0 lead before the jitters came back.
"It's not the moment to talk much about the knee," he said. He also was elusive about whether it might prevent him from playing in the season-ending ATP Finals next week in London.
"Anything can happen in one week and a half," Nadal said. "But if nothing strange happens then I'm going to be there."
Nadal was not moving with his customary speed around court in the third set but held comfortably enough for 5-2. He clinched victory on his first match point when Cuevas sent a return wide.
Nadal is guaranteed to finish the year with the top ranking for the fourth time. A maiden victory here would give him a record 31 Masters titles, one more than Novak Djokovic.
Marin Cilic of Croatia downed Roberto Bautista Agut of Spain 7-6 (4), 6-2 and next faces veteran Julien Benneteau.
Earlier in the third round, Juan Martin del Potro moved closer to securing the last spot for the finals by beating Robin Haase 7-5, 6-4.
Del Potro, who lost to Roger Federer on Sunday in the Swiss Indoors final, is in 10th place in the race to qualify for the tournament. Only the top eight players will compete in London and there is one place left, to be taken in Paris.
"I would love to reach London once again. It could be a fantastic moment for me," said del Potro, who was way back in 47th place in the race before the U.S. Open. "I'm excited to keep improving for this kind of surprise."
Del Potro has a tough challenge next, against big-serving American John Isner.
The ninth-seeded Isner, last year's runner-up to Andy Murray, hit 25 aces as he beat sixth-seeded Grigor Dimitrov of Bulgaria 7-6 (10), 5-7, 7-6 (3).
Seventh-seeded David Goffin of Belgium was through to the finals in London, despite a surprise loss to Benneteau 6-3, 6-3. The unseeded Frenchman reached the quarters of a Masters for the first time since Shanghai in 2014 in his final tournament before retiring.
Goffin will have waited nervously on the result of Frenchman Lucas Pouille's result against Jack Sock. But Pouille's 7-6 (6), 6-3 loss to the American sent him through, at Pouille's expense, making him the first Belgian to qualify for the season finale.
"I would have preferred to have qualified by winning and Lucas is a friend," Goffin said. "But I am still so happy to have qualified."
Dominic Thiem went out early again, falling to Fernando Verdasco 6-4, 6-4.
Since losing to Del Potro in the fourth round of the U.S. Open, the fifth-seeded Austrian has won only two matches in five tournaments.
Verdasco next plays Sock. Krajinovic advanced with a 6-2, 3-6, 6-1 win against Nicolas Mahut.