When West Germany's Boris Becker prepared to serve for a victory in the fifth set of their Davis Cup match here today, U.S. doubles partners Ken Flach and Robert Seguso felt a bit like lambs caught napping on the railroad tracks.

"I thought the match was over at that point," said Flach. "We got ourselves in a lot of trouble -- it was unbelievable it got down to Becker serving for the match. I thought our chances were slim and none."

Yet the two unheralded Americans somehow applied the brakes to the roaring 17-year-old West German when it counted most and came back to win a scintillating victory that sustained U.S. hopes in the Davis Cup quarterfinals.

West Germany led the playoff, 2-1, after Flach and Seguso's 6-2, 6-8, 6-1, 4-6, 7-5 defeat of Becker and Andreas Maurer. The West Germans, who took a 2-0 lead Friday, must capture only one of two singles matches Sunday to clinch their first victory over the United States in Cup play.

Nevertheless, Flach and Seguso said their snatching victory from the barrel of Becker's Wimbledon-winning serve might just give teammates Eliot Teltscher and Aaron Krickstein the impetus they need to save the playoff.

"Everyone was so inspired by that match," said Flach. "We believe in ourselves now. We believe we have a real chance to win this thing."

For the Americans, today's turnaround took a bit off the aura around Becker, who returned to West Germany as a national hero after his Wimbledon victory and opened the playoff by crushing U.S. singles leader Teltscher.

Though coming close to single-handedly winning a doubles match West Germany was expected to lose, Becker failed repeatedly on his backhand, making 19 errors on service returns, and lost three of his service games even before he failed to clinch victory in the last set.

He seemed unperturbed by his setback. Asked if he thought the loss would increase the already intense pressure on him, he merely reminded reporters that he is likely to play Krickstein in the final match Sunday, with the outcome of the quarterfinal at stake. "It's very special to be able to play when you have (that) situation," he said with an easy grin.

Today, Becker was clearly handicapped by lack of doubles experience and specifically lack of experience playing with Maurer, who is 10 years Becker's senior but far inferior in talent. Broken seven times on his serve, Maurer proved a fruitful target for the Americans as they sought to keep the ball away from Becker.

The match also was a lesson in how a practiced doubles team can win. Though almost unheard of as singles players, Flach and Seguso have become one of the five best doubles teams in the world after four years of steady play together, beginning as undergraduates at Southern Illinois.

Dressed in matching shirts, the slim Flach and chunky Seguso, both 22, deftly covered for each other on rallies and called the direction of each other's serves with behind-the-back hand signals. "We're so confident out there together," Seguso said. "We anticipate each other."

Rain also aided the Americans. After Becker and Maurer stormed back from 0-3 to win the second set and even the match, Flach and Seguso broke Becker's serve in the opening wind gusts of a storm before play was suspended. Returning after the 80-minute delay, they regained control to take another easy set.

The trouble came in the fourth set, as Becker's serve grew overpowering and the capacity crowd of 10,800 noisily cheered the West Germans. "Once they started winning, the crowd got real loud," said Flach. "It shook us up."

After Becker had put away the fourth set with a blistering service game, the West Germans broke Flach twice in the fifth set, going up the second time by 4-3. Becker was serving at 5-4 to win the match and the quarterfinal as the crowd cheered wildly in anticipation.

It was then the Americans found the chances they thought they had lost. Though Becker put in five out of six first serves, a running forehand up the middle and a lightning return by Flach from the ad court set up and then clinched the breakthrough. Defiantly shaking his fists at the chastened crowd, Flach won his serve in four straight points, and the Americans had a momentum that carried them to victory over Maurer's service.

"We thought we would win. But under the circumstances it was the most inspirational match we've had," Flach said. "It was so thrilling to win that match after being down, and to do it in the Davis Cup."