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Cape Town - Roger Federer says he will need to step it up another gear if he is to defeat countryman Stan Wawrinka in the French Open quarter-finals.
Federer became the oldest man in 28 years to make a Grand Slam last eight as he easily beat Leonardo Mayer 6-2, 6-3, 6-3 at Roland Garros.
Next up he will face compatriot Wawrinka, who came through an epic five setter against Stefanos Tsitsipas.
However, Federer knows it will not be an easy match when the two former champions collide.
"I will need to play like this again against Stan," he told reporters.
"It's fabulous that I can spend this time in Paris. I was prepared for the worst scenario, losing in the first round in three sets.
"But I am super happy with my performance. I enjoy playing here a lot. I served very well."
Results from the ninth day of the French Open on Monday (x denotes seeding):
Men
4th round
Novak Djokovic (SRB x1) bt Jan-Lennard Struff (GER) 6-3, 6-2, 6-2
Alexander Zverev (GER x5) bt Fabio Fognini (ITA x9) 3-6, 6-2, 6-2, 7-6 (7/5)
Dominic Thiem (AUT x4) bt Gael Monfils (FRA x14) 6-4, 6-4, 6-2
Karen Khachanov (RUS x10) bt Juan Martín Del Potro (ARG x8) 7-5, 6-3, 3-6, 6-3
Kei Nishikori (JPN x7) bt Benoît Paire (FRA) 6-2, 6-7 (8/10), 6-2, 6-7 (8/10), 7-5
Women
4th round
Madison Keys (USA x14) bt Katerina Siniakova (CZE) 6-2, 6-4
Ashleigh Barty (AUS x8) bt Sofia Kenin (USA) 6-3, 3-6, 6-0
Simona Halep (ROM x3) bt Iga Swiatek (POL) 6-1, 6-0
Amanda Anisimova (USA) bt Aliona Bolsova (ESP) 6-3, 6-0
