- Kerber has won both group matches
- Keys beats Cibulkova to stay in contention
- WTA Finals feature the top eight players
London (CNN)Angelique Kerber put aside her understandable end-of-season fatigue as she beat Simona Halep to close in on her first WTA semifinals spot.
Kerber struggled in her opening group match on Sunday, getting past Slovak Dominika Cibulkova in a tough three-setter.
But up against former French Open finalist Simona Halep on Tuesday, the German showed why she is the world No 1 as she wore down the light-footed Romanian with typically aggressive baseline play, 6-4, 6-2 to clinch her 61st match win of the season.
"She's always a tough opponent, and I'm very happy to have my second match win here," Kerber said in a courtside interview after beating the Romanian for the fifth time in eight matches.
Keys overpowers Cibulkova
The WTA Finals feature a round-robin format, with the top eight players in the rankings divided into two groups. Each competitor faces the three others in the group, with the top two in each section qualifying for the knockout semi-finals.
In the other match in the red group, Madison Keys posted her first ever WTA Finals victory as she blasted 26 winners past Dominika Cibulkova to win 6-1, 6-4 in just over an hour.
The 21-year-old American, who never faced a break point, remained in contention in the group after losing her opening match to Halep in straight sets. She'll face Kerber in her final group match.
It has been quite the year for Kerber, who took over the No. 1 ranking from 22-time grand slam singles winner Serena Williams after securing her first US Open tit