Mertens, number 21 in the WTA rankings, won the biggest title of her career after she defeated top seed Halep at the Qatar Open, a WTA Premier tournament at the Khalifa International Tennis and Squash Complex in Doha.

Halep controlled the first set, eventually defeating Mertens 6-3, with the Belgian having to take medical time-out for a back issue.

From here Mertens began to turn the tie around, however, triumphing in the second set 6-4.

She then secured her first WTA Premier title by winning the third set 6-3, ensuring that Halep could not stage a comeback by winning four of the final five games of the match. 

Mertens had beaten two other top 10 players on her way to the final, defeating The Netherlands' Kiki Bertens and Germany's Angelique Kerber in the quarter and semi-finals respectively. 

"Simona is a great player and it's nice to get the trophy," Mertens said.