ON A morning so pure and bright that every detail of New York seemed to have been etched in fine pencil, Martina Hingis gave youth its glorious fling with a 6-1, 3-6, 6-4 win over third seed, Arantxa Sanchez Vicario, to reach the quarter finals of the US Open.

It might have been over all the quicker if the English umpire, Jane Harvey, had not overruled a call on the Spaniard's serve at a crucial moment in the second set. The new baseline camera used by USA Network, which shoots at 800 frames per second, clearly showed the ball had dropped on the line. Harvey said it was out.

Sanchez Vicario, having been comprehensively outplayed in the first set, took that game 4-3 and Hingis immediately slewed her racket across court in an obvious show of petulance.

For some long time the 15 year old Swiss girl brooded and there appeared every chance she might spiral quickly to defeat. They had met only once before, earlier this year in America when Hingis had again taken the first set at a gallop only to lose the match.

Sanchez Vicario last won a grand slam title here in 1994 but when she levelled against Hingis few believed she would not progress.

Hingis immediately lost her serve at the start of the third set, frequently throwing her head back in disgust when she missed the line or overhit. Sanchez Vicarios danced up and down with undisguised anticipation of a quick final kill.

But Hingis is learning all the time. She broke back, playing some wonderfully fluid and mature tennis against an opponent who never knows when she is beaten. "I think I played pretty smart," said Hingis. And so she did, though that on court temper is a problem which needs to be further addressed.

However, she is less volatile than a year ago, and this was, after all, an extremely tense match against an opponent who is well known for her gamesmanship.

Hingis broke serve again for 5-3, lost her own rather nervously, and then disposed of the Spaniard a final time, instantly breaking into a jubilant jig. Sanchez Vicario's handshake was perfunctory.

There was another upset when Lindsay Davenport went down to a 2-6, 6-3, 6-0 defeat against fellow American Linda Wild. Davenport, seeded eighth and the recent winner of the Olympic gold medal in Atlanta, was quite dreadful in the opening set. She recovered her rhythm in the second and was then flushed away with startling rapidity in the third.