Safina, who arrived in Doha with a slender lead over Serena Williams in the rankings, needs to do better or match the American's performance at the season-ender to become the first Russian woman to end the year a world No.1.
Danish teenager Caroline Wozniacki survived a three-hour battle against close friend Victoria Azarenka at the WTA Championships on Wednesday to claim a 1-6, 6-4, 7-5 victory on her debut at the year-ending event.
The two big movers up the rankings this year stood toe to toe for three hours at the Khalifa Tennis Centre before Azarenka went into meltdown late in the third set after squandering two match points in their White Group clash.
World number four Wozniacki was outplayed in the first set, but the U.S. Open runner-up gradually found her range, breaking twice in a 79-minute second set to take it to a decider.
After a 10-minute heat break enforced because of temperatures still hovering in the low 30s Celsius despite darkness having long fallen over the Qatari capital, Azarenka again took command, moving into a 5-3 lead.
However, Wozniacki broke back and then saved two match points to cling on to her own serve, prompting the Belarussian to smash two racket frames in frustration.
Wozniacki seized her opportunity with relish, breaking Azarenka's serve again before serving out for victory that puts her level on one win with Azarenka who marked her debut on Tuesday with a straight sets defeat of Jelena Jankovic.
Serena Williams stayed on course to end the year as world number one when she beat Russia's Svetlana Kuznetsova 7-6, 7-5 on the opening day of the WTA Championships after sister Venus suffered a shock defeat on Tuesday.
Second-ranked Serena, who must better Dinara Safina's performance here to snatch the No 1 spot, served 11 aces under the Khalifa Stadium floodlights to get the better of the French Open champion who led 6-4 in the first-set tiebreak.
She will play Venus in her second round-robin match on Wednesday knowing that victory would almost certainly eliminate her older sibling who lost 3-6, 7-6, 6-2 to Elena Dementieva, the third Russian competing at the season-ending showpiece, in the day's outstanding contest. Eleven-times grand slam champion Serena, bidding to end the year top of the WTA rankings for the first time since 2002, was far from her best in a scrappy slug-fest against Kuznetsova.
With the match starting around 10pm local time, only a sprinkling of fans remained in the 7,000-seater Centre Court and the subdued atmosphere appeared to affect both players as they regularly found the net in high humidity. Kuznetsova looked poised to win the opening set when she came back from 1-3 down in the tiebreak to lead 6-4 but a Williams winner and an ace helped the American snuff out the danger.
