After edging Dominika Cibulkova on Sunday, world No.1 Angelique Kerber recorded her second victory in the Red Group with a 6-4 6-2 victory over Simona Halep.
After going from 1-3 to 4-3 in the first set, the third-seeded Halep lost five straight games, which translated into a 6-4 2-0 deficit. Never again did the Romanian recover and Kerber confidently won the second set, having earned another break in the fifth game.
If Dominika Cibulkova beats Madison Keys in the second Red Group match on Tuesday, Kerber will qualify for the semifinals as the group leader, while Keys gets eliminated.