By Matt Smith ABU DHABI (Reuters) - Rory McIlroy showed little rustiness as he returned from an extended break to shoot a six-under 66 and stay two strokes clear of playing partner and world number one Jordan Spieth in the first round of the Abu Dhabi Golf Championship on Thursday. Four-time major winner McIlroy's last tournament appearance was in November's DP World Tour Championship which he won to top Europe's money list for a third season in four and put a gloss on an injury-interrupted season. A year earlier, McIlroy launched his bid for the U.S. Masters, the only major he has yet to win, but instead of sealing a career grand slam he saw Spieth, 22, take both the Augusta title and later the world number one ranking. More...