World number one Novak Djokovic reached his 16th consecutive Grand Slam quarter-final on Monday to set-up a French Open quarter-final clash against evergreen Tommy Haas.
Top seed Djokovic carved out a 4-6, 6-3, 6-4, 6-4 win over 16th seed Philipp Kohlschreiber with the German paying a high price for converting just two of 13 break points.
German 12th seed Haas, meanwhile, became the third oldest man to reach the last-eight with a comfortable 6-1, 6-1, 6-3 win over volatile Russian Mikhail Youzhny.
"It's very difficult to play against Philipp as he is a specialist on clay. After the first set, I played well so I am happy," said Djokovic.
On facing Haas, against whom he has a 4-3 winning record, the Serb said: "I have a lot of respect for Tommy. He is playing well."
Djokovic, the runner-up to seven-time champion Rafael Nadal last year, needs a French Open title to complete a career Grand Slam.
The last time he failed to reach the last-eight of a major was in Paris in 2009 when he lost in the fourth round to Monday's opponent.
Haas became the first German in 17 years to reach the quarter-finals and the oldest man to make the last eight at any Grand Slam since Andre Agassi at the 2005 US Open.
Haas, who made history in the third round when he needed a record 13 match points to beat John Isner, eased past Youzhny in just 84 minutes.
"It was a pretty good performance. I was broken in the first game but I got my bearings, got into the groove," said Haas, who is enjoying a renaissance in a career which has been decimated by a series of injuries.
"He gave me a lot of unforced errors so I just kept doing what I was doing."
Only Pancho Gonzales, who was over 40 when he made the last eight in 1968, and 39-year-old Istvan Gulyas in 1971, have got this far at Haas's age in the tournament.
"The oldest since 1971? I never thought it would be possible to have this success," said Haas.
Former world number two Haas had lost on clay in straight sets to Youzhny in Rome last month.
But he was never troubled on Monday, winning 10 games in succession after losing the opener.
Such was Youzhny's frustration that he smashed his racquet nine times against his courtside chair, sending splinters spiralling into the air at Court Suzanne Lenglen.
The violence of his outburst made him an instant YouTube hit even as the match was still being played.
Haas will be the first German in the last eight in Paris since Michael Stich and Bernd Karbacher in 1996.
Later Monday, Nadal looks to celebrate his 27th birthday in style.
Nadal, bidding to be the first man to win the same Grand Slam title eight times, plays Kei Nishikori, who is trying to become just the second Japanese man to reach the last eight after Jiro Satoh, who made the quarter-finals in 1931 and 1933.
Nadal, the third seed, has a 55-1 winning record at the French Open, but his passage to the fourth round has been far from convincing after dropping the opening sets of his first two rounds for the first time in his career.
Since returning from a seven-month injury lay-off in February, the Spaniard has built up an impressive run of six titles in eight finals.
He has also won 34 of his 36 matches on clay in 2013 -- he lost to Horacio Zeballos in his first tournament back at Vina del Mar in February before seeing his eight-year winning streak at Monte Carlo ended by Djokovic in April.
Nishikori, the 13th-seed, is already the first Japanese man to reach the last 16 in Paris since Fumiteru Nakano in 1938.
Richard Gasquet, the French seventh seed, faces Stanislas Wawrinka, the ninth seed from Switzerland.
The winner of that clash will take on either Nadal or Nishikori.