In a quarterfinal match where both players had trouble holding serve, Rubin posted a 6-3, 7-6 (7-2) triumph over the defending champion and top-seeded Swiss teenager.

Rubin advanced to the Australian Open semifinals in 1996, but underwent wrist surgery in August of that year and was sidelined for three months. Last year she reached her only final at Quebec City, Canada and finished 1998 ranked No. 34.

The 23-year-old Rubin started 1999 by claiming her second career WTA Tour title at Hobart, Australia. She has won 13 of her last 15 matches and will face either Steffi Graf of Germany or Jana Novotna of the Czech Republic in Thursday's semifinals.

Hingis, who dominated Rubin, 6-1, 6-0 in their most recent meeting at last year's Lipton Championships, suffered only her third loss in 20 matches this season. After reaching the final of her first three events this year, including her third straight Australian Open title, she has lost in the quarterfinals of two straight tournaments.

No. 12 Sandrine Testud of France also earned a semifinal spot earlier today by whipping unseeded Henrieta Nagyova of Slovakia, 6-1, 6-3. On Thursday, Testud will take on either sixth seed Mary Pierce of France or surging American teenager Serena Williams, who meet later today.

Graf, the two-time champion and fifth seed, ripped Japan's Ai Sugiyama, 6-0, 6-1, on Tuesday to improve to 13-1 lifetime at this event. Novotna, the fourth seed, disposed of American qualifier Brie Rippner, 6-1, 6-4.

Graf, a 21-time Grand Slam champion and former No. 1 player, made an emotional visit here last year when she struggled in her return from knee surgery. She was moved to tears many times on her way to the semifinals last year before suffering a hamstring strain during her match with Lindsay Davenport, losing for the first time at this event.

The 29-year-old Graf will be appearing in her eighth consecutive WTA Tour quarterfinal, dating back to the fourth round at last year's U.S. Open.

Novotna has been dominated by Graf in their head-to-head meetings, winning only four of 32 matches. The reigning Wimbledon champion is competing in her first tournament since winning the Faber Grand Prix in Hannover, Germany two weeks ago.

Pierce, idle since a quarterfinal exit from the Australian Open more than a month ago, crushed Italy's Rita Grande, 6-1, 6-0, on Tuesday. Williams extended her winning streak to eight matches with a 6-0, 7-5 win over Zimbabwe's Cara Black on Tuesday.

After capturing her first WTA Tour singles title February 28 in Paris, Williams rode the momentum exactly one week later with a victory over Davenport, the second seed and 1997 champion, in the second round.

The 17-year-old Williams and older sister Venus made WTA Tour history on February 28 by becoming the first sisters to win singles titles on the same day. Serena catured the Open Gaz de France in Paris and Venus claimed the title in Oklahoma City.

First prize is $800,000.