A determined Simona Halep retained her Madrid Open title by overcoming the courageous Kristina Mladenovic 7-5 6-7 (5-7) 6-2 on Sunday (AEST).

The Romanian beat Dominika Cibulkova in straight sets in the decider of this WTA Premier event on clay 12 months ago, but she was made to work far harder by the No.14 seed this time around.

Mladenovic began to feel the effects of a back injury late in the first set, forcing her into low percentage shots that initially confounded Halep, before the favourite asserted herself against a tiring opponent to win in two hours and 43 minutes. 

It marked a 15th WTA success for the 25-year-old and was also the first time she has successfully defended a title.

Momentum swung backwards and forwards during a marathon opening set on Estadio Manolo Santana. The tone was set when Halep was broken at the end of a lengthy first game, the Romanian struggling for confidence and fluidity against her in-form opponent, who regularly put her powerful forehand to good use.

Confronted courtside by Australian coach Darren Cahill at a change of ends, Halep was implored to go after the Frenchwoman's weaker backhand and responded by slowly growing into the match, demonstrating better movement across the court and more variety in her shot-making.

Having broken back in the fourth game, Halep lost her serve again and found herself 5-3 down, but dug deep to break back again and then held to go 6-5 ahead. 

She was rewarded for her persistence when Mladenovic produced her first double fault of the match on the way to being broken, showing signs of discomfort from the back problem she carried in the final as she netted to surrender the first set.

When Halep held and then broke early in the second, she had a chance to go 3-0 ahead and take advantage of the world No.17's reduced mobility.

To her credit, Mladenovic showed huge determination to play through the pain barrier, breaking back and the second set remained on serve after that. The Frenchwoman won the subsequent tiebreak by stepping into the court and punishing Halep with those heavy forehands, celebrating passionately when she levelled it up at 1-1. 

Mladenovic's free-hitting and inventive use of volleys and drop-shots kept Halep off balance, but the world No.8's superior mobility eventually told, as she earned a double break without giving up her own serve to seal a hard-fought crown.