By Miles Evans
PARIS (Reuters) - A match-up often seen as a practice session turns deadly serious Sunday when Roger Federer plays close friend and fellow Swiss Stanislas Wawrinka for a place in the quarter-finals of the French Open.
The two, who won Swiss gold in the Olympic doubles in Beijing two years ago, face each other across the net for the first time at a grand slam, and the defending champion may not have it all his own way.
Wawrinka, the 20th seed, has beaten his illustrious compatriot on clay before and will have nothing to lose when the third match scheduled for Court Philippe Chatrier begins.
That match tops the bill in a mouthwatering program of fourth-round ties on the tournament's middle Sunday.
Jo-Wilfried Tsonga, the only home hope remaining in either singles draw, faces Russian 11th seed Mikhail Youzhny in the last match on Chatrier.
On Suzanne Lenglen, last year's runner-up Robin Soderling faces young Croatian Marin Cilic, the 10th seed, in a match sure to see some brutal hitting from the back of the court.
They are followed by British fourth seed Andy Murray, who will be aiming to reach the last eight for a second consecutive year when he faces in-form Czech Tomas Berdych, the 15th seed.
Play on Chatrier is opened by Chanelle Scheepers, the first South African to reach this stage for 13 years, who faces Russian fifth seed Elena Dementieva.
(Editing by Miles Evans)