SAINT PETERSBURG (AFP) - Top seed Belinda Bencic will face second seed Roberta Vinci in the WTA St Petersburg Ladies Trophy final after Darya Kasatkina 6-4, 6-3 in Saturday's semi-final.

Vinci, the US Open runner-up last season, overcame former French Open winner Ana Ivanovic, seeded fourth, 7-5, 6-4.

Swiss teenager Bencic, ranked 11th in the world, won her first ever WTA meeting with Russian Kasatkina to ensure she will finish the week inside the Top 10.

"It's a huge achievement for me to be in Top 10," said Bencic, 18.

"It was always like a dream for me from my early childhood. This is a very big day for me.

"Vinci is a very experienced player and it will be very tough to oppose her tomorrow as she's currently on the peak of her career, but now I'm in the top 10 and in the final so I will just enjoy it.

"Of course I want to win but I will be relaxed in the final."

The teenagers both played nervously from the start but Bencic produced fewer unforced errors and twice broke Kasatkina's serve.

The local favourite appeared still jaded from Friday's three-setter against Dominika Cibulkova, as well as her doubles duties.

Bencic broke Kasatkina's serve again halfway through the second set before serving out for the victory.

Serbian former world number one and 2008 Roland Garros champion Ivanovic started her semi-final aggressively, clinching a 3-0 lead with an early break.

But Italian Vinci broke back twice to win the opening stanza.

Vinci, ranked 16th in the world, broke in the seventh game of the second set and that proved enough for a place in her 15th WTA final.

"I'm really happy to win today," Vinci said.

"It was an incredible match, so tight at the beginning. It's always tough to play Ana because she plays so quickly. But after I was 3-0 down in the first set I forced myself to play more aggressively and it paid off."