By John O'Brien SINGAPORE (Reuters) - Angelique Kerber was forced to dig deep in her WTA Finals opener before the German world number one battled past Dominika Cibulkova 7-6(5) 2-6 6-3 in a high-class baseline slugfest at the Singapore Indoor Stadium on Sunday. Earlier, Simona Halep got her campaign off to a perfect start when the Romanian world number four dominated an erratic Madison Keys to kick off round-robin play in the elite eight-woman, season-ending event with a 6-2 6-4 victory. First-time finalist Cibulkova opened with a double fault and Kerber, who won two grand slam titles in 2016, took advantage of her opponent's nervy start to grab an immediate break without having to do much more than get the ball over the net.
Juan Martín del Potro claimed his first title since January 2014 by beating Jack Sock in straight sets to be crowned Stockholm Open champion. Del Potro has endured an injury-ravaged couple of years, but the powerful Argentine has showed great character to demonstrate what he is capable of after returning this season and was rewarded with a long-awaited tournament victory on Sunday. Del Potro took four of the nine break point opportunities that came his way, denying the world number 23 from the United States a second ATP singles title.
Richard Gasquet collected his second title of 2016 with a comfortable straight-sets victory over Diego Schwartzman at the European Open. A break in the fifth game of the match gave Gasquet an early opening in the final but he was unable to see it out easily, wasting three set points at 5-4. Schwartzman - who had disposed of three seeds on his way to Sunday's showpiece - battled back and, having broken his rival, managed to force a tie-break.