Serena Williams returns to singles tennis at Wimbledon after a year away on Tuesday as Rafael Nadal begins his quest to win the third leg of a potential calendar Grand Slam. Women's top seed Iga Swiatek, who has won her past six tournaments, will kick off proceedings on Centre Court at 1330 local time (1230 GMT) against Croatian qualifier Jana Fett. But the main focus will be on seven-time champion Williams, who faces unseeded Harmony Tan of France in her first singles match since an injury forced her to pull out of her first-round match last year.