The surly Chilean ignored a hostile centre court crowd and shrugged off the loss of the opening set to win 4-6, 6-4, 6-3, 6-3 in two hours, 38 minutes.

Yet the way the 22-year-old sprayed thumping winners around the court could only have fans of the game gasping in admiration.

Rios now plays another Spaniard, 12th-seeded Carlos Moya, who earlier beat German qualifier Jens Knippschild 6-3, 7-5, 3-6, 6-4.

Landmark victory hope

And the way to the final now appears clear for left-hander Rios, at 5ft 9in (1.75m) one of the shortest players on the ATP Tour.

He is the only surviving seed from the original top 10.

Should he triumph here, he will become the first Chilean to win a Grand Slam singles title in the Open era.

Costa had been hoping for a win to make up for his 11th-hour withdrawal from the Italian Open final two weeks ago because of a wrist injury.

But after trading the first two sets in Sunday's match, his chance was clearly slipping away from him.

Rios, who snatched the second set after recovering from 3-1 and 4-2 down, broke in the eighth game of the third with a piledriver to the back court which left Costa stranded. An ace wrapped up the set.

Crunching returns

In the fourth, Rios, bringing the full weight of his clay court armoury of strokes to bear, fought back from 0-2 down, breaking his opponent twice.

The Chilean then nearly threw away his own serve, trailing 0-40 before a disputed line call in his favour brought him back to deuce.

Costa overcame his anger and frustration at that decision to force yet another break, but Rios' crunching returns gave him the upper hand once more and he rattled off the last three games to close out the win.

Meanwhile 15th seed Spaniard Felix Mantilla made no mistakes against Paraguay's Ramon Delgado to make the last eight.

Carlos Moya also beat Jens Knippschild of Germany 6-3 7-5 3-6 6-4 and Thomas Muster of Austria knocked out Fernando Meligeni of Brazil 6-4 6-7 (8-10) 6-3 3-6 6-3.

Darkness descends on women

Two key women's fourth round matches remained unfinished as darkness descended.

Czech third seed Jana Novotna was leading Russian teenager Anna Kournikova 6-7 (2-7) 6-3 4-2 while defending champion Iva Majoli and seventh seed Conchita Martinez were deadlocked at one set all after two tie-breaks.

Fight to play Seles

Majoli won the first 7-1 and Martinez the second 7-3.

When the matches resume on Monday, Novotna and Kournikova will be bidding to play 24-year-old three-times champion Monica Seles, who beat American Chanda Rubin in straight sets, for a place in the semi-finals.

Majoli and Martinez are playing for a quarter-final showdown against second-seed Lindsay Davenport of the United States.

Davenport won through with a 6-3 4-6 6-2 victory over France's Sandrine Testud and Switzerland's Patty Schnyder eliminated Magui Serna of Spain 6-1 6-3.

Monica Seles put out Chanda Rubin 6-1 6-4 and Arantxa Sanchez-Vicario defeated Williams' younger sister, Serena 4-6 7-5 6-3.