Belinda Bencic to play Roberta Vinci in St. Petersburg Ladies Trophy final

ST. PETERSBURG, Russia -- Belinda Bencic of Switzerland beat Daria Kasatkina of Russia 6-4, 6-3 in a battle of 18-year-olds to book a St. Petersburg final against Roberta Vinci of Italy, who earlier in the day downed Serbia's Ana Ivanovic in straight sets.

Bencic came under pressure from Kasatkina but secured a win that ensures she will debut in the WTA top 10 Monday regardless of Sunday's result.

"This is a huge moment for me. To be in the top 10 is always like a dream for every small kid," said Bencic, currently ranked 11th in the world.

Kasatkina had played a tough three-set quarterfinal against Dominika Cibulkova the day before, as well as a doubles match that lasted until 1 a.m., and needed treatment on her back and stomach muscles in the second set.

In the other semifinal, Vinci rallied from a 3-0 deficit in the first set to top Ivanovic 7-5, 6-4. Vinci, ranked 16th in the world, recorded just 12 unforced errors to 29 for Ivanovic.

Vinci is 9-5 in career tour singles finals but has lost four since her last win in Palermo in 2013, including last year's US Open final. Bencic is 2-3 in WTA finals.