Local hero Kei Nishikori crashes out of Japan Open

Top seed Juan Martin del Potro and last year's finalist Milos Raonic powered Friday into the Japan Open semi-finals, but local hero Kei Nishikori's reign as champion came to a shuddering halt.

Former US Open champion del Potro beat Ukraine's Alexandr Dolgopolov 4-6, 6-4, 6-2, while third seed Raonic crushed Slovakia's Lukas Lacko 6-3, 6-3 to reach the last four of the $1.43 million Tokyo event.

A packed crowd of almost 9,000 was stunned into silence as Nishikori's 10-match winning streak on the Ariake hard-court in Japan Open and Davis Cup competition ended in back pain and bitter disappointment.

The fourth seed crashed out 7-6, 5-7, 6-3 to Spain's Nicolas Almagro.

Del Potro, runner-up in 2008, hit back superbly from a set and a break down under the floodlights against Dolgopolov to set up a semi-final with Almagro.

"I found everything difficult today in the beginning," world number seven del Potro told reporters. "He could have won the match with the break in the second set but I kept fighting and played my best tennis at the end."

Dolgopolov paid tribute to del Potro after his fifth defeat in five meetings against the giant Argentine, who is playing his first tournament since a shock second-round exit at last month's US Open.

"After I broke for 2-1 in the second set, Juan just stepped up on every shot," he said. "He started taking risks on every shot and they were all hitting the lines. The pace was unbelievable and I was just trying to hang on."

Canadian Raonic, beaten by Nishikori in last year's final, took just 62 minutes to end the fine run of Lacko, who profited to the tune of $32,000 after winning the coin toss to replace injured Frenchman Michael Llodra in the main draw.

Raonic, enjoying a purple patch after winning his fifth career title in Bangkok last weekend, blasted 11 aces and many more which put Lacko in harm's way, threatening to hit the fur off the ball at times with his bullet serve.

The world number 11 will play Ivan Dodig in the last four after the Croatian beat Finland's Jarkko Nieminen 6-2, 7-6 in the first quarter-final.

The Japan Open has had rain, muggy heat and cold conditions over the past five days.

"I've dealt well with the different conditions," Raonic told AFP. "Confidence is a big part of that. I've had hot and humid indoors, hot with the roof open and now cold.

"The court was a bit quicker today, which gave me more free points on my serve and helped pay quicker dividends."

Nishikori, who became the host country's first Japan Open winner last year, could barely move at the end of a pulsating quarter-final after pulling a back muscle.

Sixth seed Almagro -- fourth on the men's tour this season on first-serve points won behind Raonic, Sam Querrey and John Isner -- fired 15 aces and smacked several winners past Nishikori, who sportingly gave his opponent the thumbs-up after one jaw-dropping passing shot on the run.

Nishikori, his left knee taped and right ankle heavily strapped, took a medical timeout for his sore back after going up 2-1 in the third set.

With his movement badly hampered, he was broken for 5-3 before wafting a weak drop shot into the net at 0-40 and serving to stay in the match.

"At the end I put my back out and there was nothing I could do," said the world number 13. "It's been a problem for a few years. I'll have to rest and have it checked again in the off-season and find a solution."