World number one Halep was beaten in straight sets by Kanepi in round one of last year's US Open before ending her 2018 season prematurely due to a herniated disc in her back.

She came into the year's first grand slam having not won a match since August and was in danger of suffering another defeat when she dropped the first set to the powerful Kanepi.

However, Halep - whose position at the top of the rankings is under threat in Melbourne - dug deep to triumph 6-7 (2-7) 6-4 6-2 and book a second-round meeting with Sofia Kenin.

Kanepi's power posed Halep no end of problems in an opener that featured an early exchange of breaks, but the Estonian was guilty of making too many unforced errors - a natural consequence of her aggressive approach - and spurned a pair of set points on her opponent's serve when leading 6-5.

The reprieve for the 2018 runner-up proved short-lived as Kanepi dominated the subsequent tie-break to forge ahead.

Seemingly buoyed by that success, Kanepi then raised her level early in set two and broke for a 2-1 lead with the aid of eye-catching winners from each wing.

However, Halep immediately got back on level terms as Kanepi followed up the wildest of forehands with a double fault on break point.

The top seed was digging in impressively, limiting her mistakes as her rival remained erratic, and deservedly levelled the contest by converting a fourth set point as Kanepi served trailing 5-4.

Kanepi then gifted Halep a break in game six of the decider, throwing away a 40-0 lead with five successive unforced errors before taking a medical timeout for treatment on her left hand, and the end was not long in coming thereafter.