HONOLULU, HI, USA - Zhang Shuai became the last seed standing at the Hawaii Open on Friday as the singles semifinal line-up was completed before rain forced an early end to proceedings.

The Chinese top seed, finalist here last year, led Vitalia Diatchenko by a set and 4-1 before the Russian, working her way back from injury, signalled that she was unable to continue. "In sunshine and rain, I always play my best here," Zhang, 36, said, referencing the unpredictable weather on display during her match. "I love it here." 

Zhang will face Rebecca Peterson in Saturday's semifinals after the Swede brought an end to Ajla Tomljanovic's fine campaign. The Croat, who competes as an Australian in Grand Slams, had upset No.4 seed Kurumi Nara in the first round to continue a fine comeback season following shoulder surgery, but could find no answers against Peterson, going down 7-5, 7-6. Peterson, 22, is still to drop a set at this year's event.    

The only other seed in the last eight, Evgeniya Rodina, was knocked out by Julia Boserup to continue the American's fine run. Having already accounted for Sara Errani and seventh seed Misaki Doi off the back of an eight-match losing run, Boserup emerged victorious from a three-set, 96-minute thriller against No.3 seed Rodina, beating last year's semifinalist 6-1, 3-6, 6-1.

The 26-year-old, who also holds dual citizenship, spoke of the boost of seeing her mother in the crowd during her match. "It was good to look up and see her because I was not so calm," she said. "She had a very calm face."

Boserup's reward is a last-four meeting with a fellow unseeded player - South Korean Jang Su-jeong, who beat Miharu Imanishi in straight sets, 6-1, 6-3. Jang recovered from losing the first three games of the second set to become the only player to reach the semifinals in both the singles and doubles in Honolulu this week. Her singles semifinal takes places first on Saturday, ahead of Zhang's match with Peterson.