Little-known tennis player Greta Arn, who knocked top seed Maria Sharapova out of the ASB Classic, will play the defending champ in the final.
The WTA tour veteran, who represents Hungary but was born in Germany, beat German fourth seed Julia Goerges 7-6 6-3 on Friday.
The 31-year-old arrived in Auckland expecting to have to qualify, but a couple of late withdrawals put her straight into the main draw.
Arn has won only one tournament and was off the tour for about three years.
She was not expected to trouble Sharapova on Thursday, but the way she beat Goerges showed her win over the Russian former world No 1 was not a fluke.
Tough battle for Wickmayer
Arn will play defending champion Yanina Wickmayer, who had to battle hard for three sets to get past China's Shuai Peng in the earlier semifinal on Friday.
The 21-year-old won the match 3-6 7-6 7-5 after the three-hour match.
Wickmayer dropped the first set as Peng returned everything and broke her twice as the Belgian struggled with her service game.
Peng served for the match at 5-4 in the second set but Wickmayer broke back, then held to force a tiebreak which she won 7-3 with four of her points coming off Peng's serve.
The pair traded breaks in the third set until Wickmayer held for 3-1, then it went to serve and Wickmayer served for the match at 5-4.
The dogged Peng broke again - however, this time her opponent broke right back, then served it out 7-5.
Erakovic into doubles final
New Zealand's Marina Erakovic and Swedish partner Sofia Arvidsson are into the doubles final at the ASB Classic.
Erakovic and Arvidsson beat Alize Cornet, of France, and Edina Gallovits from Romania 6-3 6-1 in the semifinal on Friday.
They will play the top seeds Katarina Srebotnik, of Slovenia, and Kvetta Peschke from the Czech Republic.
The finals will be played on Saturday.