PARIS—Former world number one Roger Federer, who is targeting a record 21st Grand Slam title at Wimbledon, withdrew from the French Open on Sunday, a day after winning a tough third-round match, opting to save himself for the grass-court season. “After discussions with my team, I decided that I should withdraw from the French Open today,” Federer said in a statement released by the French Tennis Federation. “After two knee operations and more than a year of rehabilitation, it’s important that I listen to my body and not rush back into competition,” the 39-year-old Swiss added. Federer, who has hardly played in the last 17 months because of a knee injury, suffered physically in his four-set, late-night victory over German Dominik Koepfer on Saturday and decided to end his Roland Garros campaign ahead of what would have been a punishing fourth-round match against Italian Matteo Berrettini. He had said after …