FILE PHOTO: Tennis - Australian Open - Melbourne Park, Melbourne, Australia - January 11, 2019 - Romania's Simona Halep trains. REUTERS\/Edgar Su(Reuters) - Simona Halep begins her Australian Open campaign against Kaia Kanepi on Tuesday in a rematch of their U.S. Open meeting which the world number one lost in straights sets. The Romanian has struggled for form and fitness since that first-round defeat at Flushing Meadows last year and comes into the year\u2019s first Grand Slam short of preparation after a back injury ended her 2018 season prematurely. Defeat to local hope Ashleigh Barty in the opening round of the Sydney International last week means Halep has played only one match ahead of a potentially tricky test against world number 71 Kanepi. The top seed has recovered fully from a herniated disk that she aggravated at the China Open in September, but said that she was feeling a bit behind the curve. \u201cI\u2019m motivated. But it\u2019s a little bit different because last year I had about 10, 15 matches before Melbourne; now I have one, which I lost,\u201d said Halep, who reached the final at Melbourne Park last year. \u201cI took the risk staying home a little bit longer. I rested because I felt like I\u2019m exhausted after those tournaments and also the year that I had.\u201d Kanepi will be out to prove that her victory over the French Open champion was no fluke but the 33-year-old could be short of match practice herself, having not featured since reaching the fourth round in New York after aggravating an existing injury. Serena Williams, who resumes her quest for a record-equaling 24th Grand Slam title, plays unseeded German Tatjana Maria at Rod Laver Arena in the second match on Tuesday. Top seed Novak Djokovic, who made a spectacular return to form last year and won the last two Grand Slams, takes on American Mitchell Krueger in the evening session. Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Clare FallonOur Standards:The Thomson Reuters Trust Principles.