World number two Maria Sharapova won her 18th match in a row in beating Kim Clijsters 6-4 6-4 in the Red Group at the WTA Championships in Madrid.
Sharapova has not lost a match since August
Sharapova was simply too powerful for Clijsters, who had made a winning return to action in Belgium last week after two months out with injury.
US Open champion Sharapova, who could finish the season as world number one, now has one foot in the semi-finals.
The Russian 19-year-old has not lost a match since August.
"I'm definitely playing some really good tennis," Sharapova said after the match.
"I know I've played a lot of matches and I feel good about my game."
In Wednesday's other Red Group match, world number four Svetlana Kuznetsova began her Madrid campaign with a 7-5 6-3 win over fellow Russian Elena Dementieva.
After a titanic struggle in the first set, lasting 70 minutes, Kuznetsova claimed it at the third time of asking.
But one break in the second set proved enough for the former US Open champion to earn victory.
However, she said afterwards that there was room for improvement in her game.
Kuznetsova needed nearly two hours for victory
"I had a lot of chances that I didn't close out in the first set," the 21-year-old said. "I was losing my concentration, but that's normal after a long season."
Dementieva, who lost her opening match to Sharapova on Tuesday, is now almost certain to be eliminated.
The world number eight has lost her last eight matches at the season-ending tournament, having been beaten in all three of her round-robin matches in both 2004 and 2005.
In the Yellow Group, former world number one Martina Hingis kept her hopes of reaching the semi-finals alive with victory over Nadia Petrova.
Hingis, playing the season-ending event for the eighth time but for the first since leaving the women's tour in 2002, beat the Russian 6-4 3-6 6-3.
The Swiss player had also played three sets in losing her opening match against Justine Henin-Hardenne on Tuesday.
Petrova had upset world number one Amelie Mauresmo in her first match.
Hingis' win means Mauresmo cannot finish the year as world number one.
Henin-Hardenne will now finish at least third in the group and earn enough points to end Mauresmo's hopes.
Yellow Group: (1) Amélie Mauresmo (Fra), (3) Justine Henin-Hardenne (Bel), (5) Nadia Petrova (Rus), (8) Martina Hingis (Swi)
Red Group: (2) Maria Sharapova (Rus), (6) Kim Clijsters (Bel), (4) Svetlana Kuznetsova (Rus), (7) Elena Dementieva (Rus)