Rafael Nadal must up his game if he is to win an eighth French Open title after another struggle against Fabio Fognini today.
The defending champion had looked less than convincing against Daniel Brands and Martin Klizan, losing the opening set both times, and today he battled for two hours and 45 minutes.
He did not drop a set against Fognini, a flashy Italian who is consistent only in being inconsistent, but he would have done had his opponent taken his chances.
Nadal was then broken to love the first time he served for the match before eventually digging out a 7-6 (7/5) 6-4 6-4 win.
Next up for Nadal is 13th seed Kei Nishikori, who became the first Japanese man to reach the last 16 here for 75 years with a four-set victory over Benoit Paire - 6-3 6-7 6-4 6-1.
The match of the day was billed as being world number one Novak Djokovic against young pretender Grigor Dimitrov, but in fact that honour went to a remarkable five-set contest between Tommy Haas and John Isner.
Isner, who had played a five-set match yesterday, saved an incredible 12 match points in the fourth set, including nine in one game.
The American then led by a break in the fifth and had one match point himself but 35-year-old Haas clinched a 7-5 7-6 (7/4) 4-6 6-7 (10/12) 10-8 victory after four hours and 37 minutes.
Djokovic, meanwhile, took the opportunity to show Dimitrov what a long way he still has to go as he routed the Bulgarian 6-2 6-2 6-3.
Dimitrov beat Djokovic last month in Madrid but from the moment the top seed broke serve in the opening game, there never looked like being a repeat tonight.
Djokovic, who next plays Philipp Kohlschreiber, only learned after the match of the death today of his first coach, 76-year-old Jelena Gencic, who remained a very important influence in his life.
Gencic was a key figure in the early careers of Monica Seles and Goran Ivanisevic as well as Djokovic, and the 26-year-old was said to have broken down in the locker room on being told and declined to do a press conference.
Eighth seed Janko Tipsarevic is likely to find himself giving up some of his prize money after losing his temper and swearing at spectators during a 6-4 6-4 6-3 defeat by Mikhail Youzhny, who now meets Haas.
Tipsarevic said: "There is no excuse for my behaviour. I think basically the problem was that I used the F word, and that was not pretty. But on the other hand, I just snapped. It happens to everyone."
The final last-16 clash in the top half of the draw will be between seventh seed Richard Gasquet, who defeated Nikolay Davydenko 6-4 6-4 6-3, and ninth seed Stanislas Wawrinka, a 6-3 6-7 (2/7) 6-3 6-3 winner over Jerzy Janowicz.