Tracy Austin was so efficient in routing Wendy Turnbull last night in the semifinals of the $250,000 Colgate Series Championship that she nearly put 11,800 spectators at Capital Centre to sleep. But if anyone was dozing, 15-year-old Andrea Jaeger woke them up with a rousing three-set upset of defending champion Martina Navratilova.

Austin, 18, who has lost only nine games in three matches, defeated a weary Turnbull, 6-2, 6-1, in a 56-minute match that was not competitive after the third game. Austin was simply too strong from the backcourt, and undoubtedly expected a rematch against Navratolova, who overwhelmed her in last year's final, for the championship on Monday evening.

But Jaeger, playing with verve and tenacity that brought the delighted spectators to life, beat Navratilova for the second time in as many meetings, 6-4, 4-6, 6-1. Jaeger is the only player younger than Austin to have beaten her, in the quarterfinals of a tournament at Mahwah, N.J., last summer.

It was a match full of bold shot-making and psychological twists, a battle between Navratilova's heavy serve and volley artillery, which was misfiring too often for her comfort, and Jaeger's considerable weapons: a hard return of serve; particularly off the backhand; the ability to chase down apparent winners; passing shots that buzzed with topspin; spirit and court sense rare for a player so young, and a lob that just wouldn't quit.

Navratilova's powerful arsenal wore down. She was a trifle off on her touch and timing. She couldn't afford to be. Jaeger kept coming, flailing away, and ultimately, Navratilova's game collapsed under Jaeger's backcourt onslaught. Jaeger won going away.

Jaeger had won their initial meeting in Florida in the autumn, 6-1, 1-6, 6-4, but on a fast indoor carpet in a tournament of this magnitude, Navratilova figured to be an overwhelming favorite.

The expatriate Czech left-hander had looked sharp in beating Turnbull in the opening match of the tournament, then cruised into the semifinals when Chris Evert Lloyd defaulted with the flu. Jaeger walked on a tightrope to the semifinals, losing her opening match to Hana Mandlikova, then coming back from 1-5 and a match point down in the third set against Virginia Ruzici before also benefiting from Evert's withdrawal.

Last night, Jaeger always had the upper hand, but just barely, until the final set.

In the first set, Jaeger got the first break of serve in the seventh game with three forehand passing shots that foreshadowed what was to come. Navratilova broke right back to 4-4, playing her best game of the evening from the baseline, but Jaeger broke again and served out the set.

Javratilova briefly exhibited her explosive game and took a 3-0 lead in the second set, had a point for 4-0, and led 4-1.

Jaeger, her long blonde braids flying as she dashed all over the court, kept battling and broke back to 3-4 with a backhand cross-court return winner.

It seemed that Navratilova might fall apart right there, but she broke again for 5-3.She served for the set, but was broken in a bizzare game.

At 0-30 Navratilova hit an overhead and Lee Jackson, an experienced tour umpire who was in the chair, made an uncharacteristic gaffe. Not seeing that Jaeger had anticipated Navratilova's shot and was moving like the wind, the umpire called the point before it was over. Jaeger got to the ball and hit a good lob, but the point had to be replayed because of the umpire's mistake. Eventually Jaeger got the break anyway, with a running forehand passing shot off a mis-hit volley.

Navratilova looked as if she would unravel under the pressure. But she broke serve once more for the set, Jaeger hitting a forehand wide to lose a game. She was furious. She thought she had gotten two bad calls on the same sideline, and she stomped her foot and gave a pained expression that Bette Davis would have envied.

But Jaeger channeled her anger constructively, breaking Navratilova in the first game of the final set. The winning shot was one Navratilova had seen before and would see again, an excellent backhand return winner that hit six inches in from the sideline.

Jaeger could sense an upset. In holding serve for 2-0, she caught Navratilova flatfooted with another accurate lobs on the first point and served an ace down the center line for 40-15.

Navratilova held serve for 1-2, but that was her last gasp. She started to try to do too much, and nothing was working.

Jaeger held at love for 3-1, and drove in the final spike by breaking for 4-1 with a running forehand down-the-line passing shot, a heartbreaker for Navratilova. Her futility growing, the Czech tossed her racquet away before heading for the changeover.

Navratilova was getting desperate, driving returns of serve into the net or chipping them long in her anxiety to get in and volley. She planned shots that require good touch and timing, and it wasn't there. She played hard, but Jaeger was better.

In the sixth game, Jaeger was down, 0-40, on her serve and won five straight points. It was getting obvious that no matter what Navratilova tried, she could not get back in this match. Jaeger is a magnificent scrambler, and her running and gunning were just too tough.

"This is probably my biggest win," said Jaeger, who will earn at least $40,000 for her week's absense from 9th grade classes in Prarie View, Illinois, and could earn $75,000 if she beats Austin.

"Any time you play Martina on carpet, it's tough. She comes in all the time and she's a lefty -- two advantages on this surface. There are times when she serves and volleys so well that you can forget it."

Jaeger will have to be at her best to beat Austin, however, if the 18-year-old California keeps playing as she has so far. At 5-foot-4 and 110 pounds, Austin hardly looks like an irresistible force, but her groundstrokes have made her one.Just ask Turnbull.

The speedy 28-year-old Australian came into last night's match looking resolute and determined to be patient, but the depth and pace of Austin's groundstrokes kept her pinned to the back of the court and quickly discouraged her. When Austin broke for a 3-1 lead in the first set and ran off four straight games, it was all over.

Austin looked especially eager. There was a little extra bounce in the dance she always does while waiting to return serve. Meanwhile, Turnbull was exhausted after upsetting Mandilkova in three sets Friday night and then teaming with Rosemary Casals to win the doubles final, which went to 7-6 in the third set.