Rios in Japan exit

Marcelo Rios struggled to contain James Blake

Unseeded American James Blake pulled off a stunning upset to beat seventh seed Marcelo Rios of Chile and win a place in the semi-finals of the Japan Open.

The 21-year-old American served flawlessly in the last two sets for a 4-6 6-4 6-1 victory over the former world number one.

Rios broke Blake's serve in the opening game when the American's forehand hit the net cord and went wide at 30-40.

That first game was to prove costly for Blake, ranked 109th, with the first set going to Rios.

I've never played that well

James Blake

The two players held their serve until 5-4 in the second set. Blake missed his first set point at 30-40 in the 10th game when Rios fired a service winner.

But he then forced the Chilean to twice misfire his backhand to break the game and square the match at one set all.

The final set was smooth sailing for Blake who lept ahead 5-0 before Rios clawed back a game.

But Blake triumped in the 98-minute match without facing a single break point against him in the last two sets.

"(Rios) can play top 10 tennis, even number one tennis," said Blake.

"I just hung in there, got a little lucky, played some great tennis at big times at the end of the second set.

Seles secured a place in the final

"Once it was even at one set all, I knew I should try to step up and put pressure on, and when I did that, it just happened to be at the right time.

"To be honest, I've never played that well. It feels great to do that in a big tournament against a great player."

Elsewhere, top seed Lleyton Hewitt was tested by Spaniard Francisco Clavet, but the US Open champion came through in three sets to reach the semifinals.

In the women's event top seed Monica Seles overcame a sore ankle to beat Japans' Ai Sugiyama 7-5 6-4 for a place in the final.

She will meet either second seed Tamarine Tanasugarn of Thailand or eighth-seeded South African Joannette Kruger.

Seles called an injury time-out after twisting her right ankle in the first set, which the American took 7-5 after coming back from 5-4 down with Sugiyama on serve.

After trading breaks with the third seed in the second set, Seles turned up the pressure on her returns and broke to love in the 10th game to take the match in one hour 43 minutes.